Friday, 8 February 2013

Alstonite

5:46 pm OHM

Brownley Hill Mine (Bloomsberry Horse Level), Nenthead, Alston Moor District, North Pennines, North and Western Region (Cumberland), Cumbria, England, UK
© Paul Nicholson.

Formula: BaCa(CO3)2
System: Triclinic
Colour: Colourless to snow ...
Hardness: 4 - 4½
Name: After the original locality near Alston, England.
Polymorph of: Barytocalcite, Paralstonite

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Type Occurrence of Alstonite

Co-type Localities: - Brownley Hill Mine (Bloomsberry Horse Level), Nenthead, Alston Moor District, North Pennines, North and Western Region (Cumberland), Cumbria, England, UK
- Fallowfield Mine, Acomb, Hexham, Tyne Valley, Northumberland, England, UK
Place of Conservation of Type Material: Mining Academy, Freiberg, Germany, 15818.
Year of Discovery: 1841
Geological Setting of type material: Low-temperature hydrothermal deposit.

Occurrences of Alstonite

Geological Setting: Typically in low-temperature hydrothermal Pb–Zn deposits; rare in carbonatites.

Physical Properties of Alstonite

Lustre: Vitreous
Diaphaneity (Transparency): Transparent, Translucent
Colour: Colourless to snow white, yellow-gray; pale gray, pale cream, pink to pale rose-red
Comment: may fade on exposure to light; colorless in transmitted light, showing six or twelve domains
Streak: White
Hardness (Mohs): 4 - 4½
Cleavage: Imperfect/Fair
On pseudo-orthorhombic {110}, imperfect
Fracture: Irregular/Uneven
Density (measured): 3.67 - 3.711 g/cm3
Density (calculated): 3.67 g/cm3

Chemical Properties of Alstonite

Formula: BaCa(CO3)2
Essential elements: Ba, C, Ca, O
All elements listed in formula: Ba, C, Ca, O

Photos :

This sample of alstonite is displayed in the Smithsonian Museum of Natural History. Alstonite is a carbonate of barium and calciumwith the composition BaCa(CO3)2. This sample is about 12 x 12 cm and is from Alston Moor, Cumbria, England.

More Info >> Mindat: Alstonite