Montgomeryite
Current inventory:  0 gems
 

  
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)

Chemistry

Chemical Formula:

Ca₄MgAl₄(PO₄)₆(OH)₄•12(H₂O)

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

Hydrogen

2.46 %

H

22.00 %

H₂O

Oxygen

55.82 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Phosphates

Strunz 8th Ed. ID:

7/D.31-10

Nickel-Strunz 10th Ed. ID:

8.DH.25

8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H₂O
H : With large and medium-sized cations, (OH, etc.):RO₄ < 1:1

Related to:

Montgomeryite Group. Isostructural with Kingsmountite. The Mg analogue of Kingsmountite.

Varieties:

None

Synonyms:

None

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

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.

Twinning:

None

Physical Properties

Cleavage:

Perfect on {010}, Poor on {100}

Fracture:

Conchoidal

Tenacity:

Brittle

Moh's Hardness:

4.0

Density:

2.53 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Dark Green to pale Green, Colorless, Red, Yellow, may be zoned.

Transparency:

Translucent to Opaque

Luster:

Vitreous

Refractive Index:

1.572 - 1.582  Biaxial ( - )

Birefringence:

0.010

Dispersion:

Perceptible; r < v

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.

Occurances

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

View mineral photos:

Montgomeryite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

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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