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Mineralpedia Details for Alstonite

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Alstonite

Alstonite

Named for one of the two co-type localities in the Alston Moor District at the Brownley Hill mine in Cumbria, England. The other type locality for Alstonite is at the Fallowfield mine in Northumberland, England. Additional localities include in Wales, Russia, Poland, France, the United States, as well as newer localities in Namibia, Greenland, and China. Alstonite is general found in low-temperature hydrothermal lead-zinc deposits and more rarely in carbonatites. Alstonite will fluoresce yellow under short- and long-wave ultraviolet light.

Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/alstonite.pdf

Formula
BaCa(CO3)2 
Crystal System
Triclinic 
Crystal Habit
Euhedral Crystals, Pseudo Hexagonal 
Cleavage
Imperfect, None, None 
Luster
Vitreous (Glassy) 
Color
colorless, gray, white, pink 
Streak
white 
Class
Triclinic 
Fracture
Uneven 
Hardness
4-4.5 
WebMineral
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Mindat
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Alstonite from Brownley Hill Mine, Nenthead, Cumbria, England

Alstonite
            from Brownley Hill Mine, Nenthead, Cumbria, England

Large, sharp white crystals to 8mm.

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Alstonite from New Brancepeth Colliery, Deerness Valley, Durham, England

Alstonite
            from New Brancepeth Colliery, Deerness Valley, Durham, England

Good coverage of colorless to white, 1-2mm, pseudohexagonal dipyramids showing horizonatal striations. These crystals are perfectly formed and euhedral. Alstonite is the dimorph of barytocalcite. and also paralstonite. Swap Ca and Ba in the formula and you have Barytocalcite. Drop calcium all together and you get Witherite, which forms the bulk of this specimen. The Alsonite crystallization follows natural voids between Witherite crystals. The Witherite occurs as discoidal crystals to 1.3cm, but there are just a few of these. The rest of the Witherite are large anhedral forms seemingly deformed by etching. Cool specimen. It is similair to the Witherite pictured on Mindat from this locality. Note that Alstonite looks like it occurs on that one too if you look closely.

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Alstonite from Rosiclare, Hardin Co., Illinois, United States

Alstonite
            from Rosiclare, Hardin Co., Illinois, United States

Alstonite as sharp white, rice-shaped crystals to 2mm. On the side of this specimen is a vug with a yellow Fluorite crystal and thousands of colorless, perfectly terminated Alstonite crystals.

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