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| Montgomeryite
was named to honor Dr. Arthur Montgomery (1909–1999),
American mineralogist, Professor of Geology, Lafayette
College, Easton, Pennsylvania, USA, who collected the
first specimens.
| Discovered
in 1940;
IMA
status:
Valid (pre-IMA; Grandfathered) |
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Chemistry
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Chemical
Formula: |
Ca4MgAl4(PO4)6(OH)4•12(H2O) |
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Hydrated
Calcium Magnesium Aluminum Phosphate Hydroxide |
Molecular
Weight: |
1,146.58 gm |
Composition: |
Calcium |
13.98 % |
Ca |
19.56 % |
CaO |
|
Magnesium |
2.12 % |
Mg |
3.52 % |
MgO |
|
Aluminum |
9.41 % |
Al |
17.79 % |
Al2O3 |
|
Phosphorus |
16.21 % |
P |
37.14 % |
P2O5 |
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Hydrogen |
2.46 % |
H |
22.00 % |
H2O |
|
Oxygen |
55.82 % |
O |
|
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|
|
100.00 % |
|
100.00 % |
= TOTAL OXIDE |
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Classification
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Mineral
Classification: |
Phosphates
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Strunz 8th
Ed. ID:
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7/D.31-10
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Nickel-Strunz 10th
Ed. ID:
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8.DH.25
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8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
H : With large and medium-sized cations, (OH, etc.):RO4 < 1:1
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Related
to: |
Montgomeryite
Group. Isostructural with
Kingsmountite. The Mg analogue of Kingsmountite.
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Varieties: |
None
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Synonyms: |
None
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Crystal
Data
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Crystallography:
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Monoclinic
- Prismatic
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Crystal
Habit:
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Crystals lathlike, flattened on {010} and elongated and striated along
[001]; terminated by pyramids. {010} dominant, with many {hk0} vicinal
prism forms. Commonly occur in subparallel growths in contact on {010}.
Massive; as subparallel aggregates of coarse plates.
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Twinning:
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None
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Physical
Properties
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Cleavage: |
Perfect
on {010}, Poor on {100}
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Fracture: |
Conchoidal
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Tenacity:
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Brittle
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Moh's
Hardness: |
4.0
|
Density:
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2.53 (g/cm3)
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Luminescence:
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None |
Radioactivity:
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Not
Radioactive
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Optical
Properties
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Color: |
Dark
Green to pale Green, Colorless, Red, Yellow, may be
zoned.
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Transparency: |
Translucent
to Opaque
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Luster: |
Vitreous
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Refractive
Index: |
1.572
- 1.582 Biaxial ( - )
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Birefringence: |
0.010
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Dispersion: |
Perceptible;
r < v
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Pleochroism: |
Weak.
X
= colorless to pale green; Y
= Z
= colorless. May also exhibit X
= light orange brown; Y
= pale magenta-pink; Z
= light orange-brown.
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Occurances
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Geological
Setting: |
In
sedimentary phosphatic nodules (Fairfield, Utah, USA);
a late mineral in highly oxidized phosphate nodules
in granite pegmatite (South Dakota, USA). |
Common
Associations: |
Variscite,
Englishite, Wardite, Gordonite, Crandallite (Fairfield,
Utah, USA); Mitridatite, Triphylite, Rockbridgeite–Frondelite,
Whitlockite, Carbonate-Apatite, Robertsite, Fairfieldite,
Englishite (South Dakota, USA). |
Common
Impurities: |
Sr,
Ba, Fe |
Type
Locality: |
Clay Canyon, Fairfield, Oquirrh Mts, Utah County, Utah, USA
|
Year
Discovered: |
1940
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View
mineral photos: |
Montgomeryite
Mineral Photos and Locations |
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More
Information
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Mindat.org
Webmineral.com
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Montgomeryite
is a very rare phosphate mineral that is usually found
associated with Crandallite,
Variscite
and Wardite.
It was named in honor of Dr.
Arthur Montgomery (1909–1999), American mineralogist,
Professor of Geology, Lafayette College, Easton, Pennsylvania,
USA, who collected the first specimens in 1940 at Clay
Canyon, Fairfield, Oquirrh Mts., Utah, USA. It is relatively
soft with a Mohs hardness of 4.0 but takes a good polish.
Cabochons can be attractive with varying mixtures
of green Montgomeryite, yellow Crandallite, green Variscite
and white Wardite.
Montgomeryite
is found in the USA, from the Little Green Monster mine,
Clay Canyon, about nine km west of Fairfield, Utah County,
Utah; in South Dakota, in the Etta mine, near Keystone,
Pennington County, and at the Tip Top mine, 8.5 km southwest
of Custer, Custer County, South Dakota; in the Redhouse
Barite mine, Golconda district, Humboldt County, Nevada.
From the Lavra da Ilha pegmatite, in the Jequitinhonha
River, three km north of Taquaral, Minas Gerais, Brazil.
About 15 km northwest of Milgun Station, Western Australia;
in the Iron Monarch quarry, Iron Knob, and the Moculta
phosphate quarry, northeast of Angaston, South Australia.
At the Mangualde pegmatite, near Mesquitela, and the
Bendada pegmatite, near Guarda, Portugal. In Spain,
from Montcada and Bruguers, Barcelona Province. At the
Sandamap pegmatite, west of Usakos, Namibia.
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Montgomeryite
gems for sale:
We
have not photographed our Montgomeryite gems. Please
check back soon.
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