Wednesday, August 24, 2011

Mineral V


THE MINERAL VALENTINITE

Valentinite is a high lustered, often fibrous oxide mineral. It forms sprays of crystals that are usually matted to the host rock in radiating clusters. Its adamantine (gem-like) to pearly luster serves to add a nice quality to this uncommon antimony mineral.
Valentinite is dimorphous with the mineral senarmontite. Both minerals have the exact same chemistry, but they have different structures. Senarmontite is isometric and valentinite is orthorhombic. It is similar to the situation between diamond and graphite. Valentinite is associated with senarmontite as well as stibnite. Actually this association is no surprise since both senarmontite and valentinite are oxidation products of the antimony sulfide.

PHYSICAL CHARACTERISTICS:

  • Color is colorless, white, yellow, reddish or gray.
  • Luster is adamantine or pearly.
  • Transparency: Crystals are translucent to opaque in more massive specimens.
  • Crystal System is orthorhombic.
  • Crystal Habits include prismatic to fibrous and compact aggregates forming tufts and radiating sprays. Also massive and granular. Individual crystals are complexly faceted.
  • Cleavage is perfect.
  • Fracture is uneven.
  • Hardness is 2.5 - 3.
  • Specific Gravity is approximately 5.7 (heavier than average).
  • Streak is white.
  • Associated Minerals include quartz, stibnite , native antimony, senarmontite, kermesite, stibiconite and other antimony minerals.
  • Notable Occurrences include the Sensa Mine, Ain Beida, Qacentina (Constantine), Algeria; Freiberg, Germany; Dauphine, France; Bolivia; Pribram, Czech Republic; and Ham Sud Township, Wolfe County, Quebec, Canada.
  • Best Field Indicators are crystal habit, high luster, associations and specific gravity.

 

The Mineral VANADINITE

  • Chemistry: Pb5(VO4)3Cl , Lead Chlorovanadate
  • Class: Phosphates
  • Group: Apatite
  • Uses: as a minor ore of lead and mineral specimens
  • Specimens
Vanadinite shares the same structure with Apatite and the two share similar crystal shapes at times. Vanadinite is part of a chemical series with two other minerals; Pyromorphite (Pb5(PO4)3Cl) and Mimetite (Pb5(AsO4)3Cl). This series is a little different than most chemical series which involve substitution of cations such as calcium for magnesium. Instead, this series substitutes its basic chemical units the anion groups; phosphate (PO4), arsenate (AsO4) and vanadate (VO4). Vanadinite is usually red which the other members of this series and apatite group usually are not. Vanadinite's classic crystal habit is short hexagonal prisms terminated by a pinacoid, or flat basal face. These crystals are wider than they are long and are more blade-like than the barrel shaped crystals so common to the Apatite Group minerals. The high luster and deep red color give vanadinite a nice appeal to mineral collectors.

PHYSICAL CHARACTERISTICS:

  • Color is typically bright red to orange, less commonly gray or brown.
  • Luster is vitreous to adamantine.
  • Transparency crystals are transparent to translucent.
  • Crystal System is hexagonal; 6/m
  • Crystal Habit is typically the hexagonal prism with pinacoid as a termination. Rare crystals can have the hexagonal pyramid as a termination. Can also be found as rounded masses and crusts.
  • Cleavage is none.
  • Fracture is conchoidal.
  • Hardness is 3.
  • Specific Gravity is approximately 6.6+ (very heavy for translucent minerals)
  • Streak is yellowish white.
  • Associated Minerals are wulfenite, limonite, barite, galena and secondary lead deposit minerals.
  • Other Characteristics: index of refraction is 2.39 (typically high for lead minerals) and crystal terminations can be hollowed out or pitted but not as often as pyromorphite or mimetite.
  • Notable Occurances include Arizona, USA; Mexico; Tsumeb, Nambia; Zambia; and South Africa.
  • Best Field Indicators are color, crystal habit, high luster and density.

THE MINERAL VARISCITE

  • Chemistry: AlPO4-2H2O, Hydrated Aluminum Phosphate
  • Class: Phosphates
  • Group: Variscite
  • Uses: mineral specimens and ornamental stone applications
  • Specimens
Variscite is a relatively rare phosphate mineral that is sometimes confused with turquoise. It is usually greener, however, than turquoise. Variscite is sometimes used as a semi-precious stone and can make distinctive color patterns that are very attractive. Occassionally it is altered into other phosphate minerals. This can occur in what were perhaps weak layers of a nodule since only portions of the variscite nodules are altered. The most common alteration mineral is crandallite, CaAl3(PO4)2(OH)5-H2O, and gives some nodules a yellow or white layer.

PHYSICAL CHARACTERISTICS:

  • Color is light green to emerald green, sometimes bluish-green or colorless.
  • Luster is vitreous or waxy.
  • Transparency specimens are translucent.
  • Crystal System is orthorhombic; 2/m2/m2/m
  • Crystal Habits include nodules, fine grain masses, and crusts.
  • Cleavage is normally not applicable, but should be good in one direction, poor in another
  • Fracture is conchoidal, splintery, uneven.
  • Hardness is variable from 3.5 - 5
  • Specific Gravity is approximately 2.57 (average)
  • Streak is white.
  • Associated Minerals are apatite, limonite, chalcedony, crandallite, wardite and other secondary phosphate minerals.
  • Other Characteristics: alteration to other phosphate minerals causes a shrinkage, yielding gaps between variscite and these other minerals.
  • Notable Occurances include Fairfield, Utah; Germany; Australia and Brazil.
  • Best Field Indicators are color, habit, associations, density and luster.

     The Mineral VAUXITE

  • Chemistry: FeAl2(PO4)2(OH)2 - 6H2O, Hydrated Iron Aluminum Phosphate Hydroxide.
  • Class: Phosphates
  • Uses: Only as mineral specimens.
  • Specimens
Vauxite is an unusual blue-colored iron mineral. As a coloring agent in minerals, iron can produce any color in the rainbow but commonly produces reds, yellows and browns. Especially common is the red to yellow color of rust, limonite, powdered hematite and other iron oxides. This misleads many people to believe that iron can only produce these colors. But in vauxite's blue, amethyst's purple, ludlamite's apple green and other examples; this myth about iron's coloring abilities can be dispelled.
Vauxite is closely related to the often associated mineral paravauxite. Paravauxite appears to be different from vauxite only in the number of water molecules in the structure. But the presence of these water molecules alters the structure to the point that paravauxite has perfect cleavage while in sharp contrast, vauxite has no cleavage. The only other significant differences include paravauxite's green to colorless color verses vauxite's blue color.
Vauxite, paravauxite and metavauxite (a polymorph of paravauxite) are all found at the famous tin oxide deposits at Llallagua, Potosi, Bolivia. All are associated with the primary tin ore, cassiterite. They form as a result of precipitation from hydrothermal solutions.

PHYSICAL CHARACTERISTICS:

  • Color is pale to dark blue.
  • Luster is vitreous.
  • Transparency: Specimens are translucent to transparent.
  • Crystal System is triclinic.
  • Crystal Habits include tabular crystals and radiating fibrous clusters.
  • Cleavage is absent.
  • Fracture is conchoidal.
  • Hardness is 3.5
  • Specific Gravity is approximately 2.4 (average).
  • Streak is white.
  • Associated Minerals include cassiterite, metavauxite, paravauxite, wavellite, quartz and limonite.
  • Notable Occurrences are limited to the famous tin deposits at Llallagua, Potosi, Bolivia and a few minor localities around the world.
  • Best Field Indicators are color, locality, crystal habit, associations and lack of cleavage.

 

         The Mineral VERMICULITE

Vermiculite is an important member of the Montmorillonite/Smectite Group, members of which also belong to the larger general group known as the Clays. Vermiculite is also sometimes placed in the Mica Group, although recent analysis has excluded it from this group. Vermiculite is basically overly hydrated biotite or phlogopite. Natural specimens originated as these minerals and later altered to vermiculite through weathering or hydrothermal processes.
Vermiculite typically forms small platy mica like crystals. These crystals contain water in their structures and when heated to above 870° C, the water turns into steam causing the crystals to expand rapidly. The volume increase can be 2000 to even 3000%. The resulting material is then very useful for many industrial purposes. It is very lightweight, chemically non-reactive, fire resistant and odorless. Vermiculite can be used to soak up such toxic liquids as fertilizers, herbicides and insecticides. It is this ability that is also being put to good use as a bedding for pets and livestock. In addition, vermiculite can be used in concrete and ceramics as a heat resistant additive.

PHYSICAL CHARACTERISTICS:

  • Color is usually brown to golden brown, also white, colorless or yellow.
  • Luster is pearly to greasy.
  • Transparency: Crystals are translucent.
  • Crystal System is monoclinic; 2/m.
  • Crystal Habits include pseudohexagonal tabular crystals or "books", also found in compact or lamellar masses or microscopic crystals.
  • Cleavage is perfect in one direction, basal.
  • Fracture is uneven to lamellar.
  • Hardness is 1.5 (can sometimes leave marks on paper).
  • Specific Gravity is 2.3 (below average).
  • Streak is white.
  • Other Characteristics: crystals expand to many times their original volume when heated.
  • Associated Minerals include corundum, apatite, serpentine, talc, stellerite, biotite, chlorite and other clay minerals.
  • Notable Occurrences include the type locality of Milbury, Worcester County, Massachusetts, USA as well as the Rutherford quarry, Henderson County, North Carolina; Brinton's quarry, Chester County, Pennsylvania; Magnet Cove, Hot Spring County, Arkansas; California and Libby, Lincoln County, Montana, USA; Ajmer, Rajasthan, India; Phalaborwa, Transvaal, South Africa. Mud Tank, Valley Bore, Northern Territory and at Bulong, Western Australia, Australia; the Potaninskoye deposit, Southern Ural Mountains and the Kovdor massif, Kola Peninsula, Russia. Other industrial sources are in China, Brazil; Sweden; Canada and Zimbabwe.
  • Best Field Indicators are softness, color, luster and expandability when heated.

 

THE MINERAL VESUVIANITE OR IDOCRASE

  • Chemistry: Ca10(Mg, Fe)2Al4(SiO4)5(Si2O7)2(OH)4, Calcium Magnesium Iron Aluminum Silicate Hydroxide.
  • Class: Silicates
  • Subclass: Sorosilicates
  • Uses: mineral specimens and the gemstone, Idocrase
  • Specimens
Vesuvianite, also known as Idocrase, is a fascinating mineral found originally on the volcano, Mt Vesuvius, hence one of the names. The other name, idocrase, is from the greek and means mixed form, an allusion to its crystals showing a mixture of other mineral forms. The crystals belong to the tetragonal symmetry class and show a square cross-section perpendicular to the long axis. Tetragonal crystals are uncommon and vesuvianite fortunately produces some very nicely shaped crystals.
Oddly enough, some of its structure is similar to that of grossularite, a garnet, which is an isometric mineral. Its structure is also interesting in that it is composed of both SiO4 groups and Si2O7 groups. Vesuvianite could be classified as a nesosilicates because of the SiO4 groups, but the higher organization of the Si2O7 groups puts it in the sorosilicate subclass.
Vesuvianite forms as a result of contact metamorphism on impure limestones and is usually found with other exotic minerals. A massive green gem variety is called californite from where it is found. It is a somewhat rare and beautiful mineral that can rival many other minerals for interest among mineral collectors.

PHYSICAL CHARACTERISTICS:

  • Color is normally green, but also can be brown, yellow, blue and/or purple.
  • Luster is vitreous or greasy to resinous.
  • Transparency crystals are transparent to translucent.
  • Crystal System tetragonal; 4/m 2/m 2/m
  • Crystal Habits include prismatic crystals with an overall square cross-section. There is usually two sets of four sided prisms with one set being dominant. The termination is usually a four sided pyramid that can be either steeply or gently sloped. The faces of the pyramids align with the faces of the prisms making an edge that is perpendicular to the length of the crystal (as opposed to the tetragonal mineral apophyllite). A pinacoid can truncate the pyramid or form the entire termination. Massive forms are common and difficult to distinguish from massive garnet.
  • Cleavage poor, in one direction lengthwise.
  • Fracture is conchoidal to uneven.
  • Hardness is 6.5
  • Specific Gravity is 3.3 - 3.5
  • Streak is white.
  • Other Characteristics: striated lengthwise and is slightly pleochroic.
  • Associated Minerals are garnets, calcite, wollastonite, diopside and serpentine.
  • Notable Occurances Asbestos, Quebec, Canada; California and the New England region of USA; Mt Vesuvius, Italy; Ural Mountains, Russia and Switzerland.
  • Best Field Indicators crystal habit, color, cleavage and localities.

 

    THE MINERAL VESZELYITE

  • Chemistry: (Cu, Zn)3PO4(OH)3 - 2H2O , Hydrated Copper Zinc Phosphate Hydroxide.
  • Class: Phosphates
  • Uses: only as a mineral specimen.
  • Specimens
Veszelyite is a rare, but beautiful copper and zinc phosphate mineral. Specimens often command some fairly lofty prices for even diminutive specimens, which is a direct testament to veszelyite's rarity and attractiveness. It has a nice emerald-green to green-blue color and a high luster which produces a good colorful sparkle. Crystals are often randomly and individually attached on specimens much like green sprinkles that are spread on an ice cream cone. Veszelyite is truly a joy to collect.

PHYSICAL CHARACTERISTICS:

  • Color is emerald-green, green, blue or most commonly green-blue.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System is monoclinic.
  • Crystal Habits include slender prismatic, nearly wedge shaped crystals and granular aggregates.
  • Hardness is 3.5 - 4
  • Specific Gravity is approximately 3.4 (above average for translucent minerals)
  • Streak is green to greenish blue.
  • Associated Minerals include quartz and various copper and zinc secondary minerals.
  • Notable Occurrences are limited to Kipushi, Shaba, Rep. of Congo; Kabwe, Zambia; Moravicza, Banat, Romania and Black Pine Mine, Montana, USA.
  • Best Field Indicators are crystal habit, locality and color.

 

 

    THE MINERAL VILLIAUMITE

  • Chemistry: NaF, Sodium Fluoride
  • Class: Halides
  • Group: Halite
  • Uses: Rarely cut as gemstones and as mineral specimens.
  • Specimens
Villiaumite is another strongly colored Halide mineral. It has a typically bold red "carmine" color that is visually unique. Other colorful halides include fluorite (mostly purple, also green, yellow, etc), halite (pink), miersite (yellow), atacamite (green) and boleite (blue) to name a few. Villiaumite's color ranges from the strong red to reddish orange, to lavender pink. It is commonly found with colorless edges or portions that transition into the strongly colored portions of the crystal. Fluorescence is observed in many specimens, but is generally only a weak red color under both short and longwave ultraviolet light.
Villiaumite was named for the French explorer: Villiaume. Although he did not techically discover the mineral; he did collect some rock samples from Guinea in which the new mineral villiaumite was found. Villiaumite is a rare mineral and is found in only a few localities. Most massive specimens are coming from the Kola Peninsula where the mineral is associated with many other rare russian minerals such as nefedovite, lomonosovite, aegirine, fluorcaphite, pectolite, chkalovite and tuperssuatsiaite.
Another great locality for villiaumite is Mont Saint-Hilaire, Quebec, Canada where fine crystals are found. Some crystals from here have been cut as gemstones, but villiaumite is NOT a gemstone mineral as it is too soft and is not durable at all. In fact, villiaumite is soluble in water. Not exactly a property one looks for in a gemstone! Villiaumite is a sodium salt and those salts are usually soluble. And for this reason a desicant should be placed with any specimen to avoid moisture absorbtion and thus its possible destruction.
Villiaumite is a nice mineral to own. It has excellent crystal form (mostly cubes and octahedrons) and is often associated with rare and interesting minerals. Its color is unique and often bright and bold. With rarity, color, associations, fluorescence and crystal form, villiaumite has a lot going for it!

PHYSICAL CHARACTERISTICS:

  • Color is carmine red to reddish orange and lavender pink to pink. Most specimens show some colorless areas.
  • Luster is vitreous to waxy in massive specimens.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is isometric; 4/m bar 3 2/m.
  • Crystal Habits include small cubes, cubo-octahedrons and octahedrons. Also found massive and as void-filling grains.
  • Cleavage is perfect in three directions forming cubes.
  • Fracture is conchoidal.
  • Hardness is 2 - 2.5.
  • Specific Gravity is 2.8 (average)
  • Streak is pinkish white.
  • Other Characteristics: The index of refraction is 1.327, specimens are soluble in water and some specimens weakly fluoresce a red color under UV light.
  • Associated Minerals include calcite, sodalite, eudialyte, nepheline, aegirine, pectolite, lomonosovite, microcline, fluorite, loparite-(Ce), lamprophyllite, vitusite-(Ce), steenstrupine-(ce), fluorcaphite, urtite, chkalovite, tuperssuatsiaite, nefedovite and murunskite among others.
  • Notable Occurrences include the type locality: Rouma, the Islands of Los, Guinea as well as the Khibina Massif, Kola Peninsula, Russia; Aris, Namibia; Point of Rocks, Colfax County, New Mexico, USA; Mont Saint-Hilaire, Quebec, Canada and Greenland.
  • Best Field Indicators are crystal habit, color, solubility in water, occurrence, fluoresce and associations.

 

          THE MINERAL VIVIANITE

Vivianite has vibrant colors and a nice sparkle. Many clusters are found inside of fossil clam or snail shells or attached to fossil animal bone. Vivianite is not a display case type mineral. Specimens should be kept from long exposure to light as this can darken a specimen to near blackness. The reason for the darkening is from the oxidation of the iron from +2 to +3 and this change yeilds a darker specimen. The oxidation is accelerated by exposure to light. Vivianite can be enjoyed and then should be put back in a dark cabinet to preserve its beauty for years to come.

PHYSICAL CHARACTERISTICS:

  • Color is blue, green and colorless, darkens upon exposure to light.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include radiating clusters of prismatic, acicular, or fiberous crystals. Also earthy and encrusting masses. Often lines the inside of fossil shells.
  • Cleavage is perfect in one direction.
  • Fracture is splintery.
  • Hardness is 1.5 - 2.
  • Specific Gravity is approximately 2.6+ (average for translucent minerals)
  • Streak is white or bluish green.
  • Associated Minerals are siderite, sphalerite, quartz and some secondary ore deposit minerals.
  • Other Characteristics: thin crystals are flexible.
  • Notable Occurances include Maryland and Colorado, USA; Russia; Ukraine and England.
  • Best Field Indicators are color and reaction to light, flexible crystals and crystal habit.

THE MINERAL VOLBORTHITE

  • Chemistry: Cu3V2O7(OH)2 - 2H2O, Hydrated Copper Vanadate Hydroxide.
  • Class: Phosphates
  • Subclass: Vanadates
  • Uses: Only as mineral specimens.
  • Specimens
Volborthite is a rare copper vanadate mineral that was named for a Russian paleontologist; Aleksandr Fedorovich van Volborth. It was first named knaufite which is still considered a synonym. Volborthite can form encrusting masses with a beautiful yellow green coloration and pearly luster.
Volborthite is not all that closely related to the mineral calciovolborthite except that both are vanadate hydroxides. Obviously, volborthite lacks the calcium, but also has water molecules in its structure. Volborthite's formula could be written as Cu3(VO4)2 - 3H2O. But this formula does not show the true cationic unit as a pyrovanadate group; V2O7. The basic structure of volborthite is a sheet-like structure with copper oxide/hydroxide layers that are held together by the pyrovanadate groups and then these layers are stacked by layers of water.

PHYSICAL CHARACTERISTICS:

  • Color is yellow to green-yellow or light brown.
  • Luster is vitreous, pearly or dull.
  • Transparency: Specimens are translucent to opaque.
  • Crystal System is monoclinic; 2/m
  • Crystal Habit is typically encrusting or rounded masses, also individual scales. Lamellar twinning is sometimes seem.
  • Cleavage is imperfect.
  • Hardness is 3.5
  • Specific Gravity is approximately 3.4 - 3.5 (heavy for non-metallic minerals)
  • Streak is pale green.
  • Other Characteristics: Non-fluorescent.
  • Notable Occurrences include the type localities of Sisersk and Nizhne Tagilsk, Ural Mts, Russia as well as numerous localities in Arizona; Carlin Gold Mine, Nevada USA; Mt. Vesuvius, Italy; Wheal Edward, Cornwall, England; Tugao, Inuyama, Aichi, Japan; Paull's Consolidated Mine, South Australia, Australia; Pribram, Czech Republic; Copiapo, Chile; Salzburg, Austria and Vancouver Island, Canada.
  • Best Field Indicators are color, locality, non-fluorescence and density.
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