plements to _Militaer Wochenblatt_ (1878 and 1889); Siebigk,
_Selbstbiographie des Fuersten Leopold von Anhalt-Dessau_ (Dessau,
1860 and 1876); Hosaeus, _Zur Biographie des Fuersten Leopold von
Anhalt-Dessau_ (Dessau, 1876); Wuerdig, _Des Alten Dessauers Leben und
Taten_ (3rd ed., Dessau, 1903); _Briefe Konig Friedrich Wilhelms I. an
den Fuersten L._ (Berlin, 1905).

ANHYDRITE, a mineral, differing chemically from the more commonly
occurring gypsum in containing no water of crystallization, being
anhydrous calcium sulphate, CaSO_{4}. It crystallizes in the
orthorhombic system, and has three directions of perfect cleavage
parallel to the three planes of symmetry. It is not isomorphous with
the orthorhombic barium and strontium sulphates, as might be expected
from the chemical formulae. Distinctly developed crystals are somewhat
rare, the mineral usually presenting the form of cleavage masses. The
hardness is 3-1/2 and the specific gravity 2.9. The colour is white,
sometimes greyish, bluish or reddish. On the best developed of the
three cleavages the lustre is pearly, on other surfaces it is of the
ordinary vitreous type.

Anhydrite is most frequently found in salt deposits with gypsum; it
was, for instance, first discovered, in 1794, in a salt mine near
Hall in Tirol. Other localities which produce typical specimens of the
mineral, and where the mode of occurrence is the same, are Stassfurt
in Germany, Aussee in Styria and Bex in Switzerland. At all these
places it is only met with at some depth; nearer the surface of the
ground it has been altered to gypsum owing to absorption of water.

From an aqueous solution calcium sulphate is deposited as crystals
of gypsum, but when the solution contains an excess of sodium or
potassium chloride anhydrite is deposited. This is one of the several
methods by which the mineral has been prepared artificially, and
is identical with its mode of origin in nature, the mineral having
crystallized out in salt basins.

The name anhydrite was given by A.G. Werner in 1804, because of the
absence of water, as contrasted with the presence of water in gypsum.
Other 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 vulpini