Precious Stones: Lapis Lazuli, Turquoise & Malachite
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Lapis lazuli
Turquoise
Malachite and Azurite |
| Lapis
Lazuli
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Lapis Lazuli is normally a mixture of three minerals:
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Lazurite (very complex blue mineral)
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calcite (calcium carbonate, which is white)
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pyrite (an iron sulfide that is white-gold in color)
Lazurite is the essential ingredient of lapis lazuli and is the mineral
that gives it the blue color. The best quality material contains less calcite
and pyrite. Lazurite is a sodium, calcium, aluminosilicate mineral
that contains sulfur: the color is due to a charge transfer between sulfur
atoms.
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it is a felspathoid (somewhat feldspar-like)
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cubic (thus, isotropic)
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hardness: 5.5
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S.G. 2.7 - 2.9
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vitreous / greasy luster
Formation of lapis lazuli
Lapis lazuli, is a contact metamorphic rock with variable composition and
varying physical properties. It usually forms by contact
metamorphism of limestones.
Uses of lapis, durability, and simulants
Use of lapis lazuli: beads, cabochons, carvings
"Durability": sensitive to heat, acid, alkali
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sometimes dyed or coated with wax
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Swiss Lapis is dyed quartz
Comments
The name lapis is Persian for blue.
Prior to 1828, it was used as pigment for ultramarine paint.
For more that 6000 years, it has also been used as an ancient precious
stone/gem in Afghanistan, and traded throughout Africa and Europe.
Other comments
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See a movie on a lapis (sodalite) structure! |
Copper-bearing minerals formed at low temperatures: turquoise,
malacite, and azurite
Turquoise commonly occurs in veinlets penetrating weathered, aluminum -
rich, sedimentary or volcanic rocks (where it has been deposited near the
surface from circulating phosphatic waters) in arid climates, and in small,
fine-grained, rounded masses and crusts. |
Formation
of turquoise, malachite, and azurite |
Turquoise:
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turquoise is a "cryptocrystalline" material: it's made of tiny crystals
(you will rarely see individual crystals)
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it's a hydrous (water) copper (Cu) - bearing phosphate mineral
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hardness= 5 - 6
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color: medium green - blue (greener
material contains more Fe)
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greasy (waxy) luster
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other information
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Turquoise is formed in association with Cu deposits; copper is transported
in waters which interact with phosphorous and aluminum-bearing rocks.
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Turquoise is often veined and frequently contains inclusions of surrounding
rocks.
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sometimes occurs as kidney-shaped or grape-like aggregates.
Geographical:
well known deposits occur in Persia, Sinai Peninsula, China,
Chile, Egypt, Turkey, Mesoamerica (Arizona)
Comments
Other name: Turkish stone
The use of turquoise use dates back to 3000 B.C.- 4000 B.C.+ (Sinai)
Stability: sensitive to temperature: above 250 degrees C, a
loss of water leads to a dull green color
Enhancements: impregnated with plastic, parafin, oil
Synthetics: ceramic material containing small blue spheres
Simulants: glass, plastic, dyed material (e.g., calcite)--imitations
can be found from 4000 B.C.!
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View some images of malachite, azurite, and turquoise
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| Malachite and Azurite |
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Malachite:
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copper (Cu) - carbonate mineral
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soft,
green material
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hardness= 3.5 - 4.0
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S.G.: 3.75 - 3.95
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crystal system: monoclinic
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bubbles with acid
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it commonly grows as aggregates of crystals that form concentric
rings.
Geological
Cu-bearing solutions interact with carbonate rocks (cavelike deposits)
(Ancient) Uses:
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jewelry, ornaments, carving, etc.
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make up (eye shadow)
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green pigment
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cure for vomiting
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protection from witches!
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Azurite:
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Cu-bearing carbonate
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a soft, blue material
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hardness: 3.5 - 4.0
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S.G.: 3.7 - 3.9
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vitreous luster
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refractive index: 1.73 - 1.758 max. 1.838
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crystal system: masses of tiny monoclinic crystals
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occurrence: Arizona, Chile, Rhodesia
Azurite
commonly occurs with malachite (azur-malachite is an intergrowth of
the two minerals). Because of its similarity with malachite (formed in
similar way), azurite has similar physical properties and uses. |
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