Mineral U

The Mineral ULEXITE

• Chemistry: NaCaB5O6(OH)6-5H2O, Hydrated Sodium Calcium Borate Hydroxide
• Class: Carbonates
• Subclass: Borates
• Uses: an ore of boron and as mineral specimens.
• Specimens

Ulexite, like other borates, is a structurally complex mineral. The basic structure of ulexite contains chains of sodium, water and hydroxide octahedrons linked in endless chains. The chains are linked together by calcium, water, hydroxide and oxygen polyhedra and massive boron units. The basic boron unit has a formula of B5O6(OH)6 and a charge of negative three (-3). It is composed of three borate tetrahedrons and two borate triangular groups.

Ulexite is found with the mineral borax and is directly deposited in arid regions from the evaporation of water in intermittent lakes called playas. The playas form only during rainy seasons due to runoff from nearby mountains. The runoff is rich in the element boron and is highly concentrated by evaporation in the arid climate. Eventually the concentration is so great that crystals of ulexite, borax and other boron minerals form and accumulate to great thickness.

Specimens of ulexite may form a "cotton ball" tuft of acicular crystals. These can be confused with the similar appearing tufts of the silicate mineral okenite, but are of a completely different origin with completely different mineral associations.

Ulexite is also found in a vein-like bedding habit composed of closely-packed fibrous crystals. This variety is called "TV Rock" and is popular in many rock shops, especially with children. If the specimen is approximately an inch thick and is polished flat on both sides perpendicular to the fibers, then an unusual optical phenomenon can be seen. The fibers will behave like optical fibers and transmit an image from one side of the specimen to the other. In other words, a good specimen, resting on a newspaper will have the writing appear to be on top of the specimen without any distortion of the lettering. The newspaper can easily be read upon the surface of the ulexite! This is a phenomenal optical property that will stun anyone who has not seen it before. This effect is partially the result of the large spaces in the sodium octahedral chains mentioned above.

PHYSICAL CHARACTERISTICS:

• Color is white or gray to colorless.
• Luster is silky.
• Transparency crystals are transparent to translucent.
• Crystal System is triclinic; bar 1
• Crystal Habits include tufts of acicular crystals called "cotton balls". Also as vein-like masses of parallel fibrous crystals.
• Cleavage is perfect in one direction.
• Fracture is fibrous.
• Hardness is 2 (softer than a fingernail)
• Specific Gravity is approximately 1.97 (very low density)
• Streak is white.
• Associated Minerals are borax, colemanite, hydroboracite and other borate minerals.
• Other Characteristics: similar borate minerals have an alkaline taste, while ulexite is tasteless.
• Notable Occurrences include several localities in California and Nevada, USA; Tarapaca, Chile and Kazakhstan.
• Best Field Indicators are crystal habit, associations, locality, density, unique optical property, and hardness.

 

   THE MINERAL ULLMANNITE

• Chemistry: NiSbS, Nickel Antimony Sulfide
• Class: Sulfides
• Group: Cobaltite
• Uses: As a very minor ore of nickel and as mineral specimens.
• Specimens

Ullmannite, which is named for the German chemist and mineralogist, J. C. Ullmann, is a rare nickel mineral that belongs to the Cobaltite Group of minerals. Most members of this group are rare to extremely rare except for cobaltite. Like other members of this group, ullmannite can form nice crystals that are either cubic, octahedral, tetrahedral or even pyritohedral, the classic crystal form of pyrite.

Ullmannite's symmetry is isometric and it has the same unique symmetry as pyrite, skutterudite and cobaltite. They all belong to the Diploidal Class, a class that, although isometric, lacks four fold symmetry. The ullmannite structure is similar to pyrite's except that the S₂ groups of pyrite are replaced by Sb-S groups in ullmannite. The antimony and sulfur are bonded together with a covalent bond. If the antimony and sulfur have an ordered arrangement (such that all of the antimony atoms are to the left or all are to the right of the Sb-S bonds), then the symmetry is reduced to the lower symmetry of the Tetartoidal Class; 2 3. This is the lowest symmetry class of the isometric system and contains only 4 three fold and 3 two fold axes. Most ullamnnite has an unordered antimony-sulfur arrangement and therefore belongs to the higher Diploidal Class which contains 4 three fold and 3 two fold axes, three mirror planes and a center of symmetry. Even though ullmannite is known to no longer belong to this class, a synonym for the Tetartoidal Class is the term: Ullmannite Type.

Ullmanite is very similar to a nickel arsenic sulfide called gersdorffite. Gersdorffite's formula is NiAsS and shows the substitution of arsenic for the antimony in ullmannite's formula. The two elements are themselves very similar and therefore do not cause appreciable differences in their respectivly enriched minerals. The rarer ullmannite usually has some arsenic in its chemistry anyways. The two minerals are almost indistinguishable by ordinary means.

PHYSICAL CHARACTERISTICS:

• Color is steel gray, silver to tin white.
• Luster is metallic.
• Transparency: Crystals are opaque.
• Crystal System: Isometric; bar 3 2/m (if an ordered structure is found then 2 3)
• Crystal Habits include cubic, octahedral, tetrahedral and pyritohedral crystals as well as massive and granular forms.
• Cleavage is good in three directions forming cubes.
• Fracture: Uneven.
• Hardness is 5 - 5.5
• Specific Gravity is 6.6 - 6.7 (heavier than average for metallic minerals)
• Streak is black.
• Other Characteristics: Crystals are sometimes striated.
• Associated Minerals include pyrite, sphalerite, niccolite, quartz, breithauptite, calcite, galena and some iron minerals.
• Notable Occurrences include the type locality of Freusburg, Siegen, Westphalia, Germany as well as other localtions in Germany; Settlingstones Mine, North Pennines, Britain; Lolling, Carinthia, Austria; France; Brancepeth Colliery, Durham, England and Gunnison County, Colorado, USA.
• Best Field Indicators are crystal habit, cleavage, hardness and density.

 

       The Mineral URANINITE

• Chemical Formula: UO2 , Uranium Oxide
• Class: Oxides and Hydroxides
• Uses: a major ore of uranium and radium, a source of helium and as a mineral specimen
• Specimens

Uraninite is a highly radioactive and interesting mineral. It is the chief ore of uranium and radium, which is found in trace amounts. Helium was first discovered on the earth in samples of uraninite. Radium and helium are found in uraninite because they are the principle products of uranium's decay process. Weathered or otherwise altered uraninite produces some wonderful by-products such as the beautiful uranyl phosphate minerals like autunite and torbernite as well as uranyl silicates like sklodoskite and cuprosklodowskite.

The structure is analogous to the structure of fluorite, CaF2. The structure of fluorite is highly symmetrical and forms isometric crystals such as cubes and octahedrons. Flourite also has four directions of perfect cleavage that produces octahedrons. However, in uraninite, crystals are rare and the cleavage is not usually observable.

A variety of uraninite is called pitchblende which is a combination of mostly uraninite and some other minerals. It is generally softer and less dense and usually botyroidal or earthy.

Remember, this is a highly radioactive mineral and should be stored away from other minerals that are affected by radioactivity and human exposure should definitely be limited.

 

 

PHYSICAL CHARACTERISTICS:

• Color is black to steel black with tints of brown.
• Luster is submetallic to pitchy and dull.
• Transparency crystals are opaque.
• Crystal System is isometric; 4/m bar 3 2/m
• Crystal Habit is typically massive botryoidal, earthy, lamellar and reniform aggregates. Well-formed individual cubic and octahedral crystals are rare.
• Cleavage is poor in four directions (octahedral), and is rarely seen.
• Fracture is conchoidal.
• Hardness is 5 - 6
• Specific Gravity is near 10 when pure but often massive specimens are closer to 7 (heavy even for metallic minerals)
• Streak is brownish black.
• Associated Minerals include cassiterite, pyrite, native silver, autunite, uranophane, uranocircite, torbernite, meta-torbernite and other uranium minerals.
• Other Characteristics: highly radioactive!
• Notable Occurences include Bergen, Germany; Autun, France; Cornwall, England; Mitchell Co., North Carolina and Mt. Spokane, Washington, USA; Zaire; wilberforce and Great Bear Lake, Canada; Portugal and France.
• Best Field Indicators are luster, color, radioactivity and streak.

 

The Mineral URANOCIRCITE

• Chemistry: Ba(UO2)2(PO4)2-10 to 12H2O , Hydrated Barium Uranyl Phosphate
• Class: Phosphates
• Group: Autunite/Torbernite
• Uses: a very minor ore of uranium and mineral specimens
• Specimens

Uranocircite is a rare but popular mineral among collectors who seek uranium-bearing minerals. Its square tabular crystals are distinctive from the members of the autunite/torbernite group of minerals. Uranocircite's crystals are similar to other members of this group, but they tend to be flatter or not as tabular. Autunite can be difficult to distinguish from uranocircite by ordinary means. However, in the slightly heavier uranocircite, the color is usually more yellow and the fluorescent color is more green.

The structure of uranocircite is composed of phosphate tetrahedrons linked to uranium-oxygen groups that form distorted octahedrons. The phosphates and uranium groups lie in sheets that are weakly held together by water molecules. This structure produces the platy habit, the one perfect direction of cleavage, and the relative softness.

Uranocircite can lose water and convert to a different mineral called meta-uranocircite of the meta-autunite/meta-torbernite group of minerals. The change to meta-uranocircite will often produce a pseudomorph. A pseudomorph is generally an atom by atom replacement of one mineral's chemistry to form another mineral. The process leaves the crystal shape of the lost mineral intact. Pseudomorph means false (psuedo) shape (morph). In this case, the conversion is not so dramatic since it involves only the loss of a few water molecules, and therefore a good pseudomorph is likely to form. The conversion is irreversible and ongoing, and all collection specimens of a certain age are almost certainly at least partially converted.

Fine specimens should be stored in a closed container to avoid water loss. Remember, this is a radioactive mineral and should be stored away from other minerals that are affected by radioactivity and human exposure should be limited.

PHYSICAL CHARACTERISTICS:

• Colors are various shades of yellow to light yellow-green.
• Luster is vitreous to pearly on the main pinacoid.
• Transparency crystals can be transparent to translucent.
• Crystal System is tetragonal; 4/m 2/m 2/m
• Crystal Habits include platy square crystals usually in bladed aggregates. Crystals can form in parallel growths giving a "deck of cards" kind of look. Also as crusts, micaceous, foliated and scaly aggregates. Sometimes in attractive rosettes.
• Cleavage is perfect in one direction.
• Fracture is uneven.
• Hardness is 2.5
• Specific Gravity is approximately 3.5+ (above average for translucent minerals)
• Streak is a yellow tint.
• Associated Minerals are autunite, uranophane, torbernite, meta-torbernite, uraninite and other uranium minerals.
• Other Characteristics: radioactive, fluorescent green and cleavage sheets are slightly bendable.
• Notable Occurrences include Bergen, Germany; Autun, France; Cornwall, England; Mitchell Co., North Carolina and Mt. Spokane, Washington, USA; Zaire; Portugal and France.
• Best Field Indicators are color, crystal habit, fluorescence, radioactivity, associations and density.

 

    The Mineral URANOPHANE

• Chemistry: Ca(UO2)2Si2O7 - 6H2O, Hydrated Calcium Uranyl Silicate.
• Class: Silicates
• Subclass: Nesosilicates
• Uses: mineral specimen and minor ore of uranium
• Specimens

Uranophane, also known as uranotile, is a rare mineral that forms from the oxidation of uranium-bearing minerals. It is closely related to two other uranium bearing minerals cuprosklodowskite and sklodowskite, but is more common than either of them. They all form similar acicular or hair-like crystals that form radial aggregates and tufts. The color of uranophane is bright butter yellow while cuprosklodowskite is dark green and sklodowskite is a bronze to golden yellow. Uranophane forms interesting specimens and fine specimens are sought after by collectors of rare uranium minerals. Remember, this is a radioactive mineral and should be stored away from other minerals that are affected by radioactivity and human exposure should definitely be limited.

PHYSICAL CHARACTERISTICS:

• Color is usually a butter yellow to bright lemon yellow also amber to brown.
• Luster is vitreous to silky.
• Transparency: Crystals are transparent to translucent.
• Crystal System: Monoclinic.
• Crystal Habits are typically fibrous or acicular tufts, radial aggregates and crusts.
• Cleavage: perfect in one direction.
• Hardness is 2 - 3.
• Specific Gravity is approximately 3.8+ (above average for translucent minerals)
• Streak is pale yellow.
• Associated Minerals are uraninite, torbernite, autunite, zeunerite, sklodowskite, cuprosklodowskite and other uranium ore oxidation zone minerals.
• Other Characteristics: Radioactive and somewhat fluorescent greenish yellow.
• Notable Occurrences include Musonoi Mine, Shaba, Zaire; Bergen, Germany and Stone Mountain, Georgia and Hanosh Mine, New Mexico, USA.
• Best Field Indicators are crystal habit, color, associations, radioactivity and fluorescence.

 

THE MINERAL URANOPILITE

• Chemistry: (UO2)6SO4(OH)10 - 12H2O , Hydrated Uranyl Sulfate Hydroxide.
• Class: Sulfates
• Uses: a minor ore of uranium and mineral specimens
• Specimens

Uranopilite is a rare mineral but is sought after by collectors who seek uranium bearing minerals. As with many uranyl minerals, it is fluorescent and radioactive. Uranopilite fluoresces a bright green under ultraviolet light. Uranopilite is associated with other uranyl minerals such as zippeite and johannite. Uranopilite, johannite and zippeite all form as secondary minerals and as efflorescent crusts in uranium mines. Efflorescent means it forms on the surface of a rock by the evaporation of water when in contact with the dry air of the mine.

Remember, this is a radioactive mineral and should be stored away from other minerals that are affected by radioactivity and human exposure should be limited.

PHYSICAL CHARACTERISTICS:

• Colors are bright shades of yellow.
• Luster is silky.
• Transparency crystals can be transparent to translucent.
• Crystal System is monoclinic.
• Crystal Habits are usually limited to encrustations and compact masses.
• Cleavage is not seen.
• Hardness is approximately 2.
• Specific Gravity is approximately 4.0 (above average for non-metallic minerals).
• Streak is a pale yellow.
• Other Characteristics: Radioactive and fluoresces a bright green under ultraviolet light.
• Associated Minerals are uraninite, zippeite and johannite.
• Notable Occurrences include Wheal Owles, Cornwall, England; San Juan Co., Utah, USA; Northwest Territory, Canada and the Bohemian region of Europe.
• Best Field Indicators are color, crystal habit, fluorescence, softness, luster and radioactivity.

 

     THE MINERAL UVAROVITE

• Chemistry: Ca3Cr2(SiO4)3, Calcium Chromium Silicate
• Class: Silicates
• Subclass: Nesosilicates
• Group: Garnets
• Uses: Gemstones and mineral specimens
• See our natural Uvarovite Mineral Specimens
   

Uvarovite, like other garnets, forms rounded crystals with 12 rhombic or 24 trapezoidal faces or combinations of these and some other forms. This crystal habit is classic for the garnet minerals. Uvarovite is the only consistently green garnet and has a beautiful emerald-green color. As with the other calcium garnets (andradite and grossular), uvarovite is formed from the metamorphism of impure siliceous limestones and some other rocks that contain chromium. Mineral specimens of uvarovite are much sought after by collectors for outstanding brilliance and color.

PHYSICAL CHARACTERISTICS:

• Color is a bright green.
• Luster is vitreous.
• Transparency crystals are transparent to translucent.
• Crystal System is isometric; 4/m bar 3 2/m
• Crystal Habits include the typical rhombic dodecahedron. But more commonly is found as the 24 sided trapezohedron. Combinations of these forms are common. Massive and granular occurrences are also seen.
• Cleavage is absent.
• Fracture is conchoidal.
• Hardness is 6.5 - 7
• Specific Gravity is approximately 3.8 or less (above average for translucent minerals).
• Streak is white.
• Associated Minerals are chromite and serpentine.
• Other Characteristics: index of refraction is 1.86. dodecahedral faces may show striations.
• Notable Occurrences are Finland; Sarany, Ural Mountains Region, Russia; California and South Africa.
• Best Field Indicators are crystal habit, color, locality and hardness.

 

     THE MINERAL UVITE (A Tourmaline)

• Chemistry: Ca(Mg, Fe)3Al5MgSi6O18(BO3)3(OH)3, Calcium Iron Magnesium Aluminum Boro-silicate Hydroxide.
• Class: Silicates
• Subclass: Cyclosilicates
• Group: Tourmalines
• Uses: Only as mineral collection specimens
• Specimens

Uvite was considered to be a very rare member of the Tourmaline Group, but it is now becoming widely available on the mineral markets. Other more common and more well-known tourmalines are schorl (black, opaque and iron rich) and elbaite (various colors, transparent to translucent, used as a gemstone and lithium rich). less common tourmalines are dravite, liddicoatite and buergerite.

Uvite is the magnesium/iron-rich member of the group and has one notable exception to the typical tourmaline generalized formula. The usual 6 aluminums are reduced to 5, with a magnesium inserted into one of the aluminums' positions. Despite having so many coloring ions like iron and magnesium, some specimens of uvite can be colorless. The typical specimens of uvite on the mineral markets tend to be an interesting dark green to almost black in color. Other properties of uvite seem to fall in the norm for a tourmaline, except uvite tends to form stubby crystals rather than the long prismatic crystals of its close cousins. These crystals, though, are well formed and show all the interesting features that make tourmaline crystals so much fun to collect.

Uvite is a noted skarn mineral. The skarn is a term for a rock that is the product of a chemically unusual magma body that has intruded into and recrystallized a "dirty" limestone. The "dirty" limestone is not composed of just calcite, CaCO3, like "clean" limestone but is mixed with silicates and/or phosphates, etc. This mixing of the hot, chemically unusual liquids and volatiles of the magma with the different minerals of the "dirty" limestones produces some interesting and rare minerals after all the recrystallizing is done.

PHYSICAL CHARACTERISTICS:

• Color is green, colorless, white, light brown or black.
• Luster is vitreous.
• Transparency: Crystals are transparent to translucent, some dark black specimens can look opaque.
• Crystal System is Trigonal; 3 m
• Crystal Habit is typically three sided stubby almost tabular crystals. 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.
• Hardness is 7.5
• Specific Gravity is 3.0+ (average)
• Cleavage is absent although there is basal parting.
• Fracture is uneven to conchoidal.
• Streak is white.
• Other Characteristics: Strongly pleochroic and piezoelectric.
• Associated Minerals include apatite, sphene, zircon and quartz.
• Notable Occurrences is Sri Lanka; Pierrepont, New York, USA and in other Skarn localities.

Best Field Indicators are crystal habit, triangular cross-section, locality, environment, color