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| Cristobalite
is named after its first noted occurance (type locality)
of Cerro San Cristóbal, Mun. de Pachuca, Hidalgo, Mexico.
| Discovered
in 1887;
IMA
status: Valid (pre-IMA; Grandfathered) |
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Composition: |
Silicon |
46.74 % |
Si |
100.00 % |
SiO2 |
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Oxygen |
53.26 % |
O |
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100.00 % |
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100.00 % |
= TOTAL OXIDE |
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Classification
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Mineral
Classification: |
Oxides
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Strunz 8th
Ed. ID:
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4/D.01-30
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Nickel-Strunz 10th
Ed. ID:
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4.DA.15
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4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
D : Metal: Oxygen = 1:2 and similar A : With small cations: Silica family
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Related
to: |
Polymorph
of Quartz, Tridymite, Coesite and Stishovite.
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Varieties: |
None
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Synonyms: |
Cosmic
Obsidian, a-Cristobalite,
b-Cristobalite, Low Cristobalite, Lussatine
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Crystal
Data
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Crystallography:
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Tetragonal
- Trapezohedral
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Crystal
Habit:
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As
pseudo-octahedral crystals, to 4 mm, with {110} and
{331}, rarely pseudocubic. Commonly dendritic to skeletal;
as spherulites to several cm; fibrous or microcrystalline
("opal"), massive.
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Twinning:
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On
{111}, common, interpenetrant, polysynthetic, repeated.
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Physical
Properties
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Cleavage: |
None
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Fracture: |
Irregular/Uneven
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Tenacity:
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Brittle
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Moh's
Hardness: |
6.0
- 7.0
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Density:
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2.32
- 2.36 (g/cm3)
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Luminescence:
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Fluorescent;
LW UV = Green Red; LW UV = Green Red |
Radioactivity:
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Not
Radioactive
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Other: |
Thermal
properties: inverts from high- or ß-Cristobalite
at 286°C or below
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Optical
Properties
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Color: |
Colorless,
White, milky White to Yellowish, Blue-Gray, Gray; Colorless
in transmitted light.
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Transparency: |
Transparent
to Translucent
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Luster: |
Vitreous
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Refractive
Index: |
1.484
- 1.487 Uniaxial ( - )
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Birefringence: |
0.003
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Dispersion: |
None
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Pleochroism: |
None
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Occurances
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Geological
Setting: |
In
vesicles and lithophysae; a late-crystallizing phase
in basaltic to rhyolitic volcanic rocks; from acid-sulfate-type
hydrothermal alteration of volcanic rocks; precipitated
by hot springs. By contact metamorphism of sandstone;
developed during diagenesis, recrystallized from siliceous
sedimentary rocks. |
Common
Associations: |
Alunite,
Anorthoclase, Fayalite, Kaolinite, Magnetite, Opal,
Quartz, Sanidine, Tridymite |
Common
Impurities: |
Fe,
Ca, Al, K, Na, Ti, Mn, Mg, P |
Type
Locality: |
Cerro San Cristóbal, Mun. de Pachuca, Hidalgo, Mexico
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Year
Discovered: |
1887
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View
mineral photos: |
Cristobalite
Mineral Photos and Locations |
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More
Information
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|
Mindat.org
Webmineral.com
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Cristobalite
is a polymorph of all of the members of the Quartz Group
of minerals. These include Quartz, Coesite, Tridymite
and Stishovite. A polymorph means that these minerals
have the same chemistry, SiO2, but different structures.
Cristobalite is common as microscopic crystals in volcanic
rocks but larger, well formed crystals found in the
vesicles of volcanic rocks are rare. Cristobalite itself
could not be faceted, but bright white Cristobalite
crystals captured in transparent black Obsidian (as
pictured above) can make very attractive gems. These
gems have been called Cosmic Obsidian. Material from
Lipari Island, Messina Province, Sicily, Italy is the
main source of this type of gem.
Notable occurrences include the
type locality of Cerro San Cristóbal, Mun. de Pachuca, Hidalgo, Mexico; Eifel
District, Germany; the Ellora Caves, Maharashtra, India;
Lipari Island, Messina Province, Sicily, Italy; Goroyama, Japan; about 150 km north of Auckland, New
Zealand; in the USA in the San Juan Mountains, San Juan County,
Colorado; Coso Hot Springs, Inyo County, California;
near Crater Lake, Klamath County, Oregon; and many other
locations.
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Cristobalite
gems for sale:
We
have not photographed our Cristobalite gems. Please
check back soon.
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