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| Chemistry:
Ca6Al2(SO4)3(OH)12·26(H2O) [Hydrated Calcium Aluminum Sulfate Hydroxide] | Discovered
in 1874;
IMA
status: Valid (pre-IMA; Grandfathered). Ettringite
is named after the type locality at Ettringen, Rhineland-Palatinate, Germany. |
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Classification
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Mineral
Classification: |
Sulfates |
Strunz 8th
Ed. ID:
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6/D.13-10
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Nickel-Strunz 10th
Ed. ID:
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7.DG.15 |
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7 : SULFATES (selenates, tellurates, chromates, molybdates,
wolframates) D : Sulfates (selenates, etc.) with additional anions, with
H2O G : With large and medium-sized cations; with NO3,
CO3, B(OH)4, SiO4 or IO3
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Related
to: |
Ettringite
Group
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Crystal
Data
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Crystallography:
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Hexagonal
- Dihexagonal Dipyramidal
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Crystal
Habit:
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Crystals
prismatic and striated, to 20 cm, commonly unterminated,
rarely dipyramidal; may be acicular, fibrous or cottonlike.
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Twinning:
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n/a
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Physical
Properties
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Cleavage: |
[1010]
Perfect
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Fracture: |
Uneven
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Tenacity:
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Brittle
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Hardness
(Mohs): |
2.0
- 2.5
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Density:
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1.77 (g/cm3)
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Luminescence:
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None |
Radioactivity:
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Not
Radioacitve |
Other: |
Partially
soluble in water; partially dehydrates on exposure,
becoming opaque |
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Optical
Properties
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Color: |
Yellow,
pale Yellow, Colorless, milky White; turns White upon partial dehydration
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Transparency: |
Transparent
to Opaque |
Luster: |
Vitreous |
Refractive
Index: |
1.470
- 1.491 Uniaxial ( - ); changes
to Uniaxial ( + ) upon dehydration
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Birefringence: |
0.0210
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Dispersion: |
n/a |
Pleochroism: |
n/a |
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Occurances
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Geological
Setting: |
In cavities of metamorphosed limestone inclusions in a
leucite-nepheline-tephrite rock. |
Common
Associations: |
Afwillite,
Gypsum, Hydrocalumite, Mayenite, Portlandite |
Type
Locality: |
Ettringer Bellerberg Mt., Ettringen, Mayen, Eifel Mts,
Rhineland-Palatinate, Germany |
Year
Discovered: |
1824
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View
mineral photos: |
Ettringite
Mineral Photos and Locations |
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More
Information
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Mindat.org Webmineral.com
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Ettringite
is an extremely rare gem and a member of the Ettingite
Group of minerals that includes Charlesite,
Ettringite,
Sturmanite
and Thaumasite.
Ettringite crystals are usually very small so gems are
very small. Ettringite is closely related to and difficult
to distinguish from Sturmanite. Ettingite crystals are
usually found as colorless but have been found as yellow
to pale yellow from the source at the N’Chwaning
mine, Kuruman district, Cape Province, South Africa.
This location is currently the only source for gem quality
crystals. Other locations of Ettringite only produce
minute crystals too small for faceting.
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Ettringite
gems for sale:
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have not photographed the Ettringite
gems. Please
check back soon.
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