Mineral D

 

THE MINERAL DATOLITE

 

• Chemistry: CaBSiO₄(OH), Calcium Boron Silicate Hydroxide.
• Class: Silicates
• Subclass: Nesosilicates
• Group: Datolite
• Uses: As a mineral specimen, rarely as an ornamental stone and as a minor gemstone.
• Specimens

Datolite is a popular mineral among mineral collectors although it is somewhat obscure. It forms nicely faceted complex crystals. The crystals at first glance could appear to be other crystal forms such as the isometric dodecahedron or trapezohedron. However these highly symmetric crystal forms are easily distinguished from the crystals of datolite. Datolite's crystals although usually well formed and strickingly faceted lack any symmetry elements except for one mirror plane and one axis of two fold rotation.

Datolite is often found in basalt vesicles with calcite and zeolites. In fact, it is often confused with certain zeolites because of its luster, color and associations. Datolite is also found in the Lake Superior region of Michigan. It is associated with native copper at this location and is found in porcelain-like masses and nodules. The nodules are brown to off white in color and some are cut and polished as a ornamental stone.

 

PHYSICAL CHARACTERISTICS:

• Color is white, colorless, yellowish, reddish, gray, brown and green.
• Luster is vitreous to greasy.
• Transparency: Crystals are transparent to translucent.
• Crystal System: Monoclinic; 2/m
• Crystal Habits include short prismatic to wedge shaped tabular crystals with complex and richly faceted terminations. Also in porcelain-like masses that form nodules. Aggregates can be fibrous or granular.
• Cleavage is absent.
• Fracture is conchoidal to uneven.
• Hardness is 5 - 5.5
• Specific Gravity is 2.8 - 3.0
• Streak is white.
• Associated Minerals are prehnite, danburite, babingtonite, epidote, copper, calcite, quartz and zeolites.
• Notable Occurances include Russia; Lake Superior region of Michigan and Paterson, New Jersey, USA; Bancroft, Ontario, Canada; Charcas, Mexico; Schwarzwald, Germany and Norway.
• Best Field Indicators are crystal habit, absence of cleavage, hardness and color.

 

 

 

 

 The Mineral DESCLOIZITE

 

• Chemistry: PbZn(VO4)(OH) , Lead Zinc Vanadate Hydroxide
• Class: Phosphates
• Group: Descloizite
• Uses: As a minor ore of lead and zinc and as mineral specimens
• Specimens

Descloizite is the namesake of the descloizite group of minerals. The group is composed of rather rare members of which descloizite is its most common member. Descloizite is an end member of a series composed of the mineral mottramite. Mottramite is the copper rich end member while descloizite is the zinc rich member. Both minerals usually contain significant percentages of both elements and are rarely pure. Descloizite can form nice well shaped crystals that have a nice luster and striking color. Its rarity and attractiveness are the reason for the typically high prices one would expect to pay for a fine specimen.

 

PHYSICAL CHARACTERISTICS:

• Color is typically brown to reddish brown to black also yellow to orange with increase in copper content.
• Luster is greasy.
• Transparency: Crystals are transparent to opaque.
• Crystal System is orthorhombic; 2/m2/m2/m
• Crystal Habit is typically in small, flat platelets that have a rounded triangular shape or in a pyramidal form, also in tiny druzy crusts and stalactitic masses.
• Cleavage is none.
• Fracture is conchoidal to uneven.
• Hardness is 3 to 3.5.
• Specific Gravity is approximately 6.2 (very heavy for translucent minerals)
• Streak is brownish red to orange to yellow.
• Associated Minerals are wulfenite, vanadinite, mottramite, pyromorphite, and cerussite.
• Other Characteristics: Some crystals can appear arrowhead shaped.
• Notable Occurrences include Tsumeb, Nambia; Zambia; Germany; Pinal County, Arizona, and Grant County, New Mexico; U.S.A.
• Best Field Indicators are color, crystal habit, localities and density.

 

 

 

 

THE MINERAL DIABOLEITE

 

• Chemistry: CuPb₂Cl₂(OH)₄, Hydrated Copper Lead Chloride Hydroxide.
• Class: Halides
• Uses: A very minor ore of copper and lead and as mineral specimens.
• Specimens

Diaboleite's name could be interpreted from Greek as the "different" boleite. Not to be confused with the "false" boleite; named pseudoboleite. All three minerals have similar color and chemistries although boleite's is more complex and includes silver (Pb₂₆Cu₂₄Ag₁₀Cl₆₂(OH) ₄₈ - 3H₂O). Boleite was named for Boleo, Santa Rosalia, Baja California, Mexico. Diaboleite is only known from Mendip Hills, Somerset, England and a couple of localities in Arizona.

These three minerals and others with similar chemistries belong to a division in the Halides Class called the Oxyhalides and Hydroxyhalides. These minerals have oxygen and/or hydroxide groups in their respective formulas. The oxygen atom in the formula might require classification in the Oxides Class of minerals except that the structures are more tied to the halide elements and the oxygens and hydroxides are kind of superfluous to the overall structure. Some other members of the Oxyhalides and Hydroxyhalides include bideauxite, chloroxiphite, kelyanite, blixite, botallackite, laurionite, paralaurionite, mendipite, fiedlerite, pinchite, penfieldite, yedlinite, atacamite, koenenite, cumengite, zirklerite and paratacamite. Of these, only atacamite and boleite are common enough to be seen at rock shows and in rock shops with regularity.

 

PHYSICAL CHARACTERISTICS:

• Color is sky blue to dark blue.
• Luster is adamantine.
• Transparency: Crystals are usually translucent to transparent.
• Crystal System is tetragonal; bar 4 2/m
• Crystal Habits include granular crystals and encrustations.
• Cleavage is perfect.
• Fracture is conchoidal.
• Hardness is 2.5
• Specific Gravity is 5.4 - 5.5 (very heavy for translucent minerals)
• Streak is blue.
• Associated Minerals include other copper and lead minerals such as boleite, linarite, anglesite, wulfenite, phosgenite and cerussite.
• Notable Occurrences are limited to the Mammoth-St. Anthony and Rowley Mines of Arizona, USA and the type locality of Higher Pitts Mine, Mendip Hills, Somerset, England.
• Best Field Indicators are color, density, fracture, streak and locality.

 

 

THE MINERAL DIAMOND

 

• Chemistry: C, Elemental Carbon
• Class: Native Elements
• Subclass: Non-metallics
• Group: Carbon
• Uses: as a gemstone and abrasive.
• We sell natural diamond mineral Specimens
• For jewelry, visit our Affiliates

Diamond is the ultimate gemstone, having few weaknesses and many strengths. It is well known that Diamond is the hardest substance found in nature, but few people realize that Diamond is four times harder than the next hardest natural mineral, corundum (sapphire and ruby). But even as hard as it is, it is not impervious. Diamond has four directions of cleavage, meaning that if it receives a sharp blow in one of these directions it will cleave, or split. A skilled diamond setter and/or jeweler will prevent any of these directions from being in a position to be struck while mounted in a jewelry piece.

As a gemstone, Diamond's single flaw (perfect cleavage) is far outdistanced by the sum of its positive qualities. It has a broad color range, high refraction, high dispersion or fire, very low reactivity to chemicals, rarity, and of course, extreme hardness and durability. Diamond is the April Birthstone.

In terms of its physical properties, diamond is the ultimate mineral in several ways:

• Hardness: Diamond is a perfect "10", defining the top of the hardness scale.
• Clarity: Diamond is transparent over a larger range of wavelengths (from the ultraviolet into the far infrared) than is any other solid or liquid substance - nothing else even comes close.
• Thermal Conductivity: Diamond conducts heat better than anything - five times better than the second best element, Silver!
• Melting Point: Diamond has the highest melting point (3820 degrees Kelvin)!
• Lattice Density: The atoms of Diamond are packed closer together than are the atoms of any other substance!

Diamond is a polymorph of the element carbon. Graphite is another polymorph. The two share the same chemistry, carbon, but have very different structures and properties. Diamond is hard, Graphite is soft (the "lead" of a pencil). Diamond is an excellent electrical insulator, Graphite is a good conductor of electricity. Diamond is the ultimate abrasive, Graphite is a very good lubricant. Diamond is transparent, Graphite is opaque. Diamond crystallizes in the Isometric system and graphite crystallizes in the hexagonal system. Somewhat of a surprise is that at surface temperatures and pressures, Graphite is the stable form of carbon. In fact, all diamonds at or near the surface of the Earth are currently undergoing a transformation into Graphite. This reaction, fortunately, is extremely slow.

 

PHYSICAL CHARACTERISTICS:

• Color is variable and tends toward pale yellows, browns, grays, and also white, blue, black, reddish, greenish and colorless.
• Luster is adamantine to waxy.
• Transparency crystals are transparent to translucent in rough crystals.
• Crystal System is isometric; 4/m bar 3 2/m
• Crystal Habits include isometric forms such as cubes and octahedrons, twinning is also seen.
• Hardness is 10
• Specific Gravity is 3.5 (above average)
• Cleavage is perfect in 4 directions forming octahedrons.
• Fracture is conchoidal.
• Streak is white.
• Associated Minerals are limited to those found in kimberlite rock, an ultramafic igneous rock composed mostly of olivine.
• Other Characteristics: refractive index is 2.4 ( very high), dispersion is 0.044, fluorescent.
• Notable Occurrences include South Africa and other localities throughout Africa, India, Brazil, Russia, Australia, and Arkansas.
• Best Field Indicator is extreme hardness.

 

THE MINERAL DIGENITE

 

• Chemistry: Cu9S5, Copper Sulfide.
• Class: Sulfides
• Uses: As an important ore of copper and as mineral specimens.
• Specimens

Digenite is an important ore of copper, although it is not very well known even by mineral collectors. The reasons for this lack of appreciation for digenite could be due to the fact that it does not generally form good crystals, lacks brilliant colors and is easily confused with other copper sulfides. But as is the case for any mineral that rarely forms good crystals, the specimens that do show good crystal habit are in exceptional demand.

 

PHYSICAL CHARACTERISTICS:

• Color is blue or black.
• Luster is submetallic.
• Transparency crystals are opaque.
• Crystal System is isometric.
• Crystal Habits are limited to mostly massive and granular components of massive sulfide rocks, but a few localities have produced good crystals.
• Hardness is 2.5 - 3
• Specific Gravity is approximately 5.6 (above average for metallic minerals)
• Associated Minerals include pyrite, chalcocite, bornite and chalcopyrite.
• Notable Occurrences include many mines around the world that contain copper sulfides such as in Sweden; Australia; South-West Africa and several copper mines in Arizona, Butte Montana and Kennecott, Alaska, USA.
• Best Field Indicators are color, associations, softness and density.

 

 

 

 

 

 THE MINERAL DIOPSIDE

 

• Chemistry: CaMgSi2 O6, Calcium Magnesium Silicate
• Class: Silicates
• Subclass: Inosilicates
• Group: Pyroxenes
• Uses: occasionally used as a gemstone and as a mineral specimen.
• Specimens

Diopside is an important rock forming mineral in several metamorphic and basic to ultra basic igneous rocks, also found in meteorites. Diopside is a part of an important solid solution series of the pyroxene group. The series includes the minerals hedenbergite, CaFeSi2 O6, and augite, (Ca, Na)(Fe, Mg, Al)(Al, Si)2 O6. A series occurs when ions (in this case iron and magnesium) can freely substitute between each other. Diopside is the magnesium rich end member of the series. The diopside-hedenbergite series is analogous to the amphiobole, tremolite- actinolite series.

Diopside has several varieties, including a chromium-rich gem variety called chrome diopside. Violan is rare blue variety found in some localities in Italy. There is also a green "cat's eye" variety that contains minute inclusions, probably of rutile, that reflect light in such a way as to produce a lively linear luminscence within the crystal. Still another variety is quite dark, with included rutile needles aligned so as to produce a 4-rayed star, hence the name star diopside. Ordinary diopside is typically white or green and can have a nice glassy luster. While the color of chrome diopside is much brighter, many specimens of ordinary diopside are also cut for gemstones. Mineral specimens of diopside can be very striking in appearance, and of interest to mineral collectors.

 

 

PHYSICAL CHARACTERISTICS:

• Color is clear, white, blue, bright and pale green to yellowish or greenish brown.
• Luster is vitreous.
• Transparency crystals are transparent to translucent.
• Crystal System is monoclinic; 2/m
• Crystal Habits include short prismatic, rarely tabular crystals. The square cross section is distinctive in the prismatic crystals. Also compact, granular, columnar and massive.
• Cleavage is perfect in two lengthwise directions at close to right angles and a basal parting direction is sometimes seen.
• Fracture is uneven, even rough.
• Hardness is 5 - 6
• Specific Gravity is approximately 3.3 (slightly above average)
• Streak is white.
• Other Characteristics: Some specimens have been known to fluoresce and some specimens have inclusions that can form "cat's eyes" if polished in cabachon.
• Associated Minerals are grossular, andradite, fluorite, dolomite, chlorite, vesuvianite, phlogopite, actinolite, olivine, iron meteorites and calcite.
• Notable Occurrences include St. Lawrence Co., New York, USA; Ural Mountains, Russia; Mt. Vesuvius and other locallities in Italy; Austria; Germany; Sri Lanka; Brazil; Mogok, Burma; Madagascar; Kimberly, South Africa and Outokumpu, Finland.
• Best Field Indicators are crystal habit, associations, color, fracture and cleavage.

 

 

 

THE MINERAL DIOPTASE

 

• Chemistry: CuSiO3 -H2O, Hydrated copper silicate.
• Class: Silicates
• Subclass: Cyclosilicates
• Uses: mineral specimen, rarely a gemstone and a very minor ore of copper.
• Specimens

Dioptase is a very beautiful mineral and it is one of the few minerals that can challenge the peerlessness of emerald's deep green. Unfortunately it is rather soft (for a gemstone) and has good cleavage and therefore is not usually cut as a gemstone. The mineral specimens that dioptase produces, however, are truly a treasure for anyone that likes deep green colors.

Dioptase is one of the few silicates to crystallize in the same symmetry class as dolomite and forms crystals that can have a typical carbonates' rhombohedral shape. Dioptase shares this symmetry with the typically ice clear silicate phenakite and the fluorescent but rarely well crystallized willemite.

Specimens of dioptase are often deeply colored and show well developed crystals. The faces of the rhombohedrons, and even the prism faces, are very reflective due to a fairly high luster. Crystals can be quite clear but at times they seem to be cloudy due to the deep color. The special attributes of a high quality specimen of dioptase are hard to describe adequately but must be observed in person in order to appreciate their value. Fine crystals of dioptase are still available in large supplies but their sources are few and the continued demand may put a squeeze on their abundance in the future.

 

PHYSICAL CHARACTERISTICS:

• Color is deep green.
• Luster is vitreous.
• Transparency crystals are transparent to translucent.
• Crystal System is trigonal; bar 3 (Dioptase is one of the few rhombic silicates).
• Crystal Habits include stubby crystals that are usually well formed prisms topped with the three faces of a rhombohedon. Prisms are six sided and usually not very long. Simple rhombohedrons are also common, at times a second rhombohedron will modify the primary rhombohedron faces producing a second set of three smaller faces. Crusts and massive forms are also seen.
• Cleavage is perfect in three directions forming rhombohedrons.
• Fracture is conchoidal and brittle.
• Hardness is 5 (harder than other green copper minerals).
• Specific Gravity is approximately 3.3+ (slightly above average)
• Streak is green.
• Associated Minerals are dolomite, calcite, cerussite, limonite, chrysocolla and other copper minerals.
• Other Characteristics: index of refraction is 1.65 - 1.71.
• Notable Occurrences include Tsumeb, Nambia; Zaire; Russia; California and Arizona, USA and Chile.
• Best Field Indicators are crystal habit, deep color and hardness.

 

 

 

 

DOLOMITE

 

• Chemistry: CaMg(CO3)2, Calcium Magnesium Carbonate
• Class: Carbonates
• Group: Dolomite
• Uses: in some cements, as a source of magnesium and as mineral specimens.
• Specimens

Dolomite, which is named for the French mineralogist Deodat de Dolomieu, is a common sedimentary rock-forming mineral that can be found in massive beds several hundred feet thick. They are found all over the world and are quite common in sedimentary rock sequences. These rocks are called appropriately enough dolomite or dolomitic limestone. Disputes have arisen as to how these dolomite beds formed and the debate has been called the "Dolomite Problem". Dolomite at present time, does not form on the surface of the earth; yet massive layers of dolomite can be found in ancient rocks. That is quite a problem for sedimentologists who see sandstones, shales and limestones formed today almost before their eyes. Why no dolomite? Well there are no good simple answers, but it appears that dolomite rock is one of the few sedimentary rocks that undergoes a significant mineralogical change after it is deposited. They are originally deposited as calcite/aragonite rich limestones, but during a process call diagenesis the calcite and/or aragonite is altered to dolomite. The process is not metamorphism, but something just short of that. Magnesium rich ground waters that have a significant amount of salinity are probably crucial and warm, tropical near ocean environments are probably the best source of dolomite formation.

Dolomite in addition to the sedimentary beds is also found in metamorphic marbles, hydrothermal veins and replacement deposits. Except in its pink, curved crystal habit dolomite is hard to distinguish from its second cousin, calcite.But calcite is far more common and effervesces easily when acid is applied to it. But this is not the case with dolomite which only weakly bubbles with acid and only when the acid is warm or the dolomite is powdered. Dolomite is also slightly harder, denser and never forms scalenohedrons (calcite's most typical habit).

Dolomite differs from calcite, CaCO3, in the addition of magnesium ions to make the formula, CaMg(CO3)2. The magnesium ions are not the same size as calcium and the two ions seem incompatible in the same layer. In calcite the structure is composed of alternating layers of carbonate ions, CO3, and calcium ions. In dolomite, the magnesiums occupy one layer by themselves followed by a carbonate layer which is followed by an exclusively calcite layer and so forth. Why the alternating layers? It is probably the significant size difference between calcium and magnesium and it is more stable to group the differing sized ions into same sized layers. Other carbonate minerals that have this alternating layered structure belong to the Dolomite Group. Dolomite is the principle member of the Dolomite Group of minerals which includes ankerite, the only other somewhat common member.

Dolomite forms rhombohedrons as its typical crystal habit. But for some reason, possibly twinning, some crystals curve into saddle-shaped crystals. These crystals represent a unique crystal habit that is well known as classical dolomite. Not all crystals of dolomite are curved and some impressive specimens show well formed, sharp rhombohedrons. The luster of dolomite is unique as well and is probably the best illustration of a pearly luster. The pearl-like effect is best seen on the curved crystals as a sheen of light can sweep across the curved surface. Dolomite can be several different colors, but colorless and white are very common. However it is dolomite's pink color that sets another unique characteristic for dolomite. Crystals of dolomite are well known for their typical beautiful pink color, pearly luster and unusual crystal habit and it is these clusters that make very attractive specimens.

 

PHYSICAL CHARACTERISTICS:

• Color is often pink or pinkish and can be colorless, white, yellow, gray or even brown or black when iron is present in the crystal.
• Luster is pearly to vitreous to dull.
• Transparency crystals are transparent to translucent.
• Crystal System is trigonal; bar 3
• Crystal Habits include saddle shaped rhombohedral twins and simple rhombs some with slightly curved faces, also prismatic, massive, granular and rock forming. Never found in scalenohedrons.
• Cleavage is perfect in three directions forming rhombohedrons.
• Fracture is conchoidal.
• Hardness is 3.5-4
• Specific Gravity is 2.86 (average)
• Streak is white.
• Other Characteristics: Unlike calcite, effervesces weakly with warm acid or when first powdered with cold HCl.
• Associated Minerals: include calcite, sulfide ore minerals, fluorite, barite, quartz and occasionally with gold.
• Notable Occurrences include many localities throughout the world, but well known from sites in Midwestern quarries of the USA; Ontario, Canada; Switzerland; Pamplona, Spain and in Mexico.
• Best Field Indicators are typical pink color, crystal habit, hardness, slow reaction to acid, density and luster.

 

 

 

 

 THE MINERAL DOMEYKITE

 

• Chemistry: Cu₃As, Copper Arsenide
• Class: Sulfides
• Subclass: Arsenides
• Uses: Mineral specimens, ornamental stone and as a minor ore of copper.
• Specimens

Domeykite is a semi-metal alloy of copper and arsenic. It is found at several copper mines in Chile and is named for a nineteenth century Chilean mineralogist named Ignacio Domeyko. Alloys are usually placed in the Elements Class. But domeykite is placed in the Sulfide Class because arsenic is chemically similar to sulfur.

Domeykite can be used in many similar ways to those of native copper. Not only is it used as a minor ore of copper, it is also used for similar ornamental purposes. It is cut and polished and made into attractive cabochons, clocks, bookends and carvings. Its metallic luster and odd color make it a very unusual ornamental stone.

 

PHYSICAL CHARACTERISTICS:

• Color is off-white, yellow-brown, copper-brown to steel-gray.
• Luster is metallic.
• Transparency: Crystals are opaque.
• Crystal System: Isometric, possibly tetragonal; bar 4 2/m.
• Crystal Habits include botryoidal, reniform and massive specimens.
• Cleavage: Absent.
• Fracture: Hackly.
• Hardness is 3 - 3.5
• Specific Gravity is variable from 7.2 to 8.1 but averages around 7.7 (very heavy even for metallic minerals).
• Streak is gray black.
• Other Characteristics: Specimens will tarnish easily and cutting or powdering specimens will yield a garlic odor (arsenic).
• Associated Minerals include calcite, nickeline, copper and other copper ore minerals.
• Notable Occurrences include the type locality of Algodones Mine, Coquimbo, Chile and also the Mohawk Mine, Keweenaw County, Michigan, USA and the copper mines of Ontario, Canada.
• Best Field Indicators are color, crystal habit, streak, density and luster.

 

THE MINERAL DRAVITE

(Tourmaline)

 

• Chemistry: NaMg3(Al,Fe)6Si6O18(BO3)3(OH)4, complex Sodium Magnesium Iron Boro-Aluminium Silicate
• Class: Silicates
• Subclass: Cyclosilicates
• Group: Tourmalines
• Uses: mineral collection specimens
• Specimens

Dravite is a little known species of the Tourmaline Group. Two other tourmalines are Schorl (black, iron rich) and Elbaite (various colors and sometimes cut for gems, lithium rich). Dravite will sometimes produce rather large well shaped crystals that are important specimens in a rock hound's collection.

 

PHYSICAL CHARACTERISTICS:

• Color is light brown to dark brown.
• Crystal Habit is typically elongated three sided prisms. The terminations can be either a simple to complex trigonal pyramid or a flat basal face. The prism faces are striated lengthwise. In cross section, all tourmalines will appear predominantly triangular in shape with some crystals showing a hexagon. Doubly terminated crystals are hemimorphic meaning that the two ends of the crystal are not exactly alike. Massive forms can also be found.
• Transparency: crystals are translucent to opaque.
• Crystal System is Trigonal; 3m
• Hardness is 7 - 7.5
• Specific Gravity is 3.2+ (slightly heavier than average)
• Cleavage is absent although there is basal parting.
• Fracture is uneven to conchoidal.
• Luster is vitreous.
• Associated Minerals include those associated with metamorphic rocks such as micas, feldspars and quartz.
• Other Characteristics: crystals are brittle and refractive indices = 1.62 and 1.68 .
• Notable Occurances include brazil and some other South American countries, and Africa.
• Best Field Indicators are crystal habit, triangular cross-section, color and hardness.

 

THE MINERAL DUFRENITE

 

• Chemistry: Fe5(PO4)3(OH)5 - 2H2O, Hydrated Iron Phosphate Hydroxide.
• Class: Phosphates
• Uses: Only as mineral specimens.
• Specimens

Dufrenite is a classic phosphate mineral. It is known from classic localities in Devon, England and elsewhere. Often associated with other rare minerals, dufrenite specimens can easily be a collectors favorite. Although not particularly colorful unless fresh, dufrenite's muted yellowish-brown color is none-the-less unique and distinctive. In fact, it produces a nice backdrop to the more colorful minerals that may be attached to the rounded botryoidal landscape.

 

 

 

 

PHYSICAL CHARACTERISTICS:

• Color is yellowish-green or olive when fresh but turns brown when oxidized.
• Luster is varied from vitreous or silky to dull or earthy.
• Transparency: Specimens are translucent to transparent.
• Crystal System is monoclinic; 2/m
• Crystal Habits include botryoidal and globular masses or tabular crystals. Also found in radiating clusters and crusts.
• Cleavage is perfect in two directions.
• Fracture is uneven.
• Hardness is 3.5 - 4.5
• Specific Gravity is approximately 3.1 - 3.3 (slightly above average).
• Streak is yellow-green.
• Associated Minerals include hureaulite, laubmannite, kidwellite, quartz, limonite and rockbridgeite.
• Notable Occurrences include Cornwall, England; Westphalia, Germany; Anglar, France and Cherokee County, Alabama, USA.
• Best Field Indicators are crystal habit, color, associations and streak.

 

 

 

 

  

THE MINERAL DUFTITE

 

• Chemistry: (Pb, Ca)(Cu, Zn)AsO4(OH), Lead Calcium Copper Zinc Arsenate Hydroxide
• Class: Phosphate Class
• Subclass: Arsenates
• Group: Adelite
• Uses: Only as mineral specimens
• Specimens

Duftite is an oxidation product of weathered ore deposits. It is often associated with other beautiful and/or rare oxidation minerals. The formula is typically written without the calcium and zinc as these elements are not always a significant percentage of the mineral.

The color of duftite gives it its great note of distinction. The color is usually an attractive green of one shade or another. It seems that the color is often difficult to label and is given a variety of pleasant names. It has been described as pea-green, apple-green, gray-green, olive-green, lime green and dark green. Whatever the shade, it usually is quite attractive and a joy to possess in one's collection.

 

PHYSICAL CHARACTERISTICS:

• Color is olive-green, gray-green or simply green.
• Luster is vitreous.
• Transparency: Crystals are transparent to translucent.
• Crystal System is Orthorhombic.
• Crystal Habits include microcrystalline crusts and small tabular crystals.
• Cleavage is indistinct.
• Fracture is uneven.
• Hardness is 3.
• Specific Gravity is approximately 6.4 - 6.6 (heavy for translucent minerals)
• Streak is white.
• Associated Minerals include wickenburgite, diopside, quartz, shattuckite, crocoite, ajoite, minium, cerussite, azurite, calcite, wulfenite and malachite.
• Notable Occurrence include Tsumeb, Namibia; E-Z Mine, Puttapa, Australia and Maricopa, County, Arizona, USA.
• Best Field Indicators are crystal habit, color, density, non-colored streak and localities.

 

THE MINERAL DUMORTIERITE

 

• Chemistry: Al_{6.5 - 7}(BO₃)(SiO₄)₃(O, OH)₃, Aluminum Boro-silicate Hydroxide.
• Class: Silicates
• Subclass: Nesosilicates
• Uses: As an ornamental and semi-precious stone, in the manufacture of high grade ceramics and porcelain and as mineral specimens.
• Specimens

Dumortierite is a boro-silicate mineral that is used as a popular ornamental stone. It has a deep violet to blue color that is very attractive and unusual. Although it is not used as a gemstone due to a lack of clarity, it does have good hardness and a bright color. Massive dumortierite can be carved into cabochons, beads, sculptures, eggs and spheres. A variety of quartz called dumortierite quartz is massive quartz colored blue by included crystals of dumortierite. Dumortierite can be misidentified as other ornamental stones such as sodalite, lazurite and lazulite. Blue sodalite has more white portions and is much lighter in density. Lazurite and lazulite are not fibrous. In China, some dumortierite has been used as an imitation lapis lazuli in carvings.

Dumortierite is related to several other nesosilicate boro-silicates such as grandidierite, harkerite, holtite, kornerupine, magnesiodumortierite, prismatine and werdingite. Dumortierite is far more common than all of these. In fact, it is the most common boro-silicate with the exception of the more common members of the Tourmaline Group. Dumortierite is commonly found in aluminum rich metamorphic rocks in contact metamorphic regions and in some pegmatites. It can alter to the mineral pyrophyllite. Dumortierite is named for the French paleontologist, Eugene Dumortier.

 

PHYSICAL CHARACTERISTICS:

• Color is typically blue to violet, but also pink and brown.
• Luster is vitreous to dull.
• Transparency: Crystals are translucent to transparent, massive specimens are nearly opaque.
• Crystal System is orthorhombic; 2/m 2/m 2/m.
• Crystal Habits include prismatic crystals but more commonly massive, columnar and fibrous.
• Cleavage good in one direction and poor in four others, but rarely seen.
• Fracture is uneven to hackly.
• Hardness is 7 - 8.5
• Specific Gravity is 3.3 - 3.4
• Streak is bluish white.
• Other Characteristics: Crystals are pleochroic from red to blue to violet. Some specimens fluoresce a blue color under longwave UV light with a fluorescent yellow matrix and a few specimens from Oreana, Nevada have fluoresced white under shortwave UV light.
• Associated Minerals are numerous and include quartz, kyanite, sillimanite, staurolite, andalusite, muscovite, lazulite and pyrophyllite
• Notable Occurrences include the type locality of Beaunan, France as well as Quartzite, La Paz County, Arizona; Colorado; Oreana, Nevada; New York, New York and Alpine, San Diego County and Los Angeles County, California, USA; Magadanskaya, Siberia, Russia and Sahatany, Madagascar.

 

 

 

 

  

THE MINERAL DUNDASITE

 

• Chemistry: Pb2Al4(CO3)4(OH)8 - 3H2O, Hydrated Lead Aluminum Carbonate Hydroxide.
• Class: Carbonate
• Uses: As a very minor ore of lead and as mineral specimens.
• Specimens

Dundasite, which is named for the famous mines at Dundas, Tasmania, Australia where it is found, is a rare lead aluminum carbonate mineral. It is found with other lead minerals such as cerussite and crocoite. Cerussite is similar in color to dundasite but is significantly heavier. Crocoite is probably the most famous mineral from the Dundas mines and has a bright orange to red color. Together with the snow white crusts of dundasite and the striking color of crocoite, the combination makes for attractive mineral specimens.

 

PHYSICAL CHARACTERISTICS:

• Color is white.
• Luster is vitreous to silky.
• Transparency: Crystals are transparent to translucent.
• Crystal System is orthorhombic.
• Crystal Habits: Generally limited to crusts and small aggregates of radiating acicular crystals.
• Hardness is 2
• Specific Gravity is 3.5 (somewhat heavy for translucent minerals)
• Cleavage is perfect in one direction.
• Fracture is uneven.
• Streak is white.
• Associated Minerals include cerussite and crocoite.
• Notable Occurrences include Dundas, Tasmania, Australia and Wensley, Derbyshire and Trefriw, Gwynedd, Wales, England.
• Best Field Indicators are locality, softness, density, color and crystal habit.

 

 

 

 

THE MINERAL DYSCRASITE

 

• Chemistry: Ag3Sb, Silver Antimonide
• Class: Sulfides
• Subclass: Antimonides
• Uses: Mineral specimens and as a minor ore of silver.
• Specimens

Dyscrasite is a very interesting, rare and beautiful silver mineral that is popular with collectors who love to collect silver bearing minerals especially micromounted specimens. Dyscrasite is actually an alloy of the silver and antimony which means the atoms of silver and antimony are combined with metallic bonds instead of ionic or covalent bonds. Alloys are usually placed in the Elements Class. But dyscrasite is placed in the Sulfide Class because antimony is really a semi-metal and not a metal like silver.

Dyscrasite forms intricate and strikingly beautiful crystals and crystal aggregates. Its metallic silver-white color rivals the beautiful color of silver itself. The crystals, although usually quite small, are never-the-less quite detailed and reminiscent of something out of this world. Forms include arborescent (branching) and cyclic pseudo-hexagonal twinned crystals. Dyscrasite is locally an important ore of silver.

 

PHYSICAL CHARACTERISTICS:

• Color is silver-white.
• Luster is metallic.
• Transparency: Crystals are opaque.
• Crystal System: Orthorhombic; 2/m 2/m 2/m.
• Crystal Habits include intricate arborescent and prismatic striated crystals. Cyclic twinned crystals are pseudo-hexagonal (six-sided) prisms and pyramids, but these are especially rare. Commonly found massive.
• Cleavage: Not discernible.
• Fracture: Hackly.
• Hardness is 3.5 - 4
• Specific Gravity is 9.4 - 10 (very heavy for metallic minerals).
• Streak is silver.
• Other Characteristics: Specimens will tarnish to a yellow or black color with exposure to light.
• Associated Minerals include calcite, silver and silver ore minerals.
• Notable Occurrences include Wolfach and the Harz Mountains of Germany; Pribram, Czech Republic; Broken Hill, New South Wales, Australia; Pima and Santa Cruz Counties, Arizona, USA; Atacama, Chile and Cobalt, Ontario, Canada.
• Best Field Indicators are crystal habit, streak, density, color, tarnish and luster.