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Mansfieldite
Current inventory:  0 gems
 

Chemistry:  Al(AsO₄)·2(H₂O) [Hydrated Aluminum Arsenate]

Discovered in 1948;   IMA status: Valid (pre-IMA; Grandfathered).
Mansfieldite is named for Dr. George Rogers Mansfield (1875-1947), geologist, U. S. Geological Survey.

Classification

Mineral Classification:

Arsenate

Strunz 8th Ed. ID:

7/C.09-70

Nickel-Strunz 10th Ed. ID:

8.CD.10

8 : PHOSPHATES, ARSENATES, VANADATES
C : Phosphates without additional anions, with H₂O
D : With only medium-sized cations, RO₄:H₂O = 1:2

Related to:

Variscite Group. Mansfieldite - Scorodite Series. The aluminum analogue of Scorodite.

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal

Crystal Habit:

Rarely in pseudo-octahedral crystals, to 2 mm; commonly as crusts, and porous to cellular masses with spherulitic structure.

Twinning:

None

Physical Properties

Cleavage:

[201] Imperfect/Fair, [001] Imperfect

Fracture:

Sub-Conchoidal

Tenacity:

Brittle

Hardness (Mohs):

3.5 - 4.0

Density:

3.03 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Health Warning:

CAUTION: Contains Arsenic, a poisonous element - always wash hands after handling. Avoid inhaling dust when handling or breaking. Never lick or ingest.

Optical Properties

Color:

White to pale Gray, light Green to Bluish Green

Transparency:

Opaque to Semi-Transparent

Luster:

Vitreous

Refractive Index:

1.622 - 1.663  Biaxial ( + )

Birefringence:

0.0200 - 0.0320

Dispersion:

Strong; r > v

Pleochroism:

None

Occurances

Geological Setting:

A hydrothermal product in altered and mineralized andesitic pyroclastic rocks (Hobart Butte, Oregon, USA).

Common Associations:

Kaolinite, Quartz, Realgar, Scorodite, Stibnite (Hobart Butte, Oregon, USA)

Type Locality:

Hobart Butte, Black Butte District, Lane Co., Oregon, USA

Year Discovered:

1948

View mineral photos:

Mansfieldite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Mansfieldite is a very rare phosphare mineral that is usually found as opaque to semi-transparent crusts or in massive form. It is extremely rare to find pseudo-octahedral crystals and these are very small, to 2 mm. Its coloring is typically white to pale gray, light green to bluish green and rarely shades of pink when cobalt bearing.

There are very few localities for finding Mansfieldite. Some of these are Djebel Debar, northeast of Hammam Meskhoutine, Qacentina (Constantine), Algeria; on Mt. Cobalt, 110 km south of Cloncurry, Queensland, Australia; and in the Bota-Burum uranium deposit, 15 km southwest of Alakol Lake, Chu-Ili Mountains, southwestern Balkhash district, Kazakhstan.
 

  
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