Everything about Anhydrite totally explained
Anhydrite is a mineral - anhydrous
calcium sulfate, CaSO
4. It is in the
orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of
symmetry. It isn't isomorphous with the orthorhombic
barium (
baryte) and
strontium (
celestine) sulfates, as might be expected from the chemical formulas. Distinctly developed
crystals are somewhat rare, the mineral usually presenting the form of cleavage masses. The hardness is 3.5 and the specific gravity 2.9. The colour is white, sometimes greyish, bluish or purple. On the best developed of the three cleavages the lustre is pearly, on other surfaces it's vitreous. When exposed to water, anhydrite readily transforms to the more commonly occurring
gypsum, (CaSO
4·2H
2O) by the absorption of water. Anhydrite is commonly associated with
calcite,
halite, and
sulfides such as
galena,
chalcopyrite,
molybdenite and
pyrite in vein deposits.
Anhydrite is most frequently found in
evaporite deposits with gypsum; it was, for instance, first discovered, in 1794, in a salt mine near Hall in
Tirol. In this occurrence depth is critical since nearer the surface anhydrite has been altered to gypsum by absorption of circulating ground water.
From an aqueous
solution calcium sulfate is deposited as crystals of gypsum, but when the solution contains an excess of
sodium or
potassium chloride anhydrite is deposited if temperature is above 40°C. This is one of the several methods by which the mineral has been prepared, and is identical with its mode of origin in nature, the mineral is common in salt
basins.
The name anhydrite was given by
A. G. Werner in
1804, because of the absence of water of crystallization, as contrasted with the presence of water in gypsum. Some obsolete names for the species are muriacite and karstenite; the former, an earlier name, being given under the impression that the substance was a chloride (muriate). A peculiar variety occurring as contorted concretionary masses is known as tripe-stone, and a scaly granular variety, from
Vulpino, near
Bergamo, in
Lombardy, as vulpinite; the latter is cut and polished for ornamental purposes.
Chicken-wire anhydrite
Chicken-wire anhydrite is a type of anhydrite deposit where seeping ground water gradually deposited large amounts of anhydrite in the sediment, replacing most of it, so that a cross-section of it looks somewhat like the coarse wire netting often used to confine
poultry.
Further Information
Get more info on 'Anhydrite'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://anhydrite.totallyexplained.com">Anhydrite Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
