30 
Hydrate of magnesia, brucite —The primary form is an 
hexagonal prism, white, passing into green and grey, more 
frequently occurring in radiated-foliated masses, of TO—T5 
hardness, and 2 "35 specific gravity ; it is a simple hydrate 
of magnesia, Mg H, which is dissolved without efferves¬ 
cence in acids, and occurs at Swinaness in the Isle of 
Unst, Shetland, and at Hoboken in New Jersey. 
Meerschaum is the name given to a hydrous silicate of 
magnesia = Mg Si + H, occurring in dense white masses, 
of an earthy appearance, which feels light, adheres to the 
lips when wetted, and therefore possesses a low specific 
gravity of T27—T6 ; the hardness varies from 2"5—3"0. 
It is found in dense masses in Livadia and Natolia, also 
at Hrubschiitz in Moravia. When freshly dug it is tough, 
and may be kneaded to a dough, out of which the cele¬ 
brated pipe-heads are manufactured. That from Natolia 
is especially valued for this purpose. 
Steatite or Soapstone, Spanish Chalk is a similar silicate 
of magnesia, which sometimes contains a small quantity of 
clay and oxide of iron. It is, however, unctuous to the 
touch, and sometimes occurs in altered crystals of quartz— 
as for example at Gopfersgrun in Bayreuth, and, in dense 
masses, it is employed in the manufacture of all kinds of 
objects of art, for polishing glass and marble, etc. 
Figs. 7—10. Gypsum, Selenite. 
Gypsum crystallizes in oblique rectangular or right 
rhombic prisms, as its primary form, inasmuch as the 
crystals can be placed on a rectangular (Fig. 7), or on a 
rhomboidal plane. Truncations of the greater basal 
edges and of the lateral edges (Fig. 8) are, however, fre¬ 
quently found; yet more frequently twins arising from 
the aggregation of two such crystals (Fig. 9), or large len¬ 
ticular twins, which present wedge-shaped forms (Fig. 10). 
The latter variety occurs especially fine at Montmartre, 
near Paris, the former principally in the beds of rock-salt 
at Bex, in the county of Maadt in Salzburg, in the 
lower beds of shell-limestone in Swabia and Thuringia, 
in many English localities, and elsewhere. Very large 
crystals, often remarkably curved, are found in Coburg 
and in Oxfordshire. Gypsum is found, fibrous and of 
silky lustre, especially fine at Aargau, in Nottingham, and 
Derby, also in the marl of Swabia, etc.; a foliated variety 
occurs imbedded in the common earthy or lamellar gyp¬ 
sum. Common gypsum is found in almost all limestone 
rocks and clay marls in the stratified formations, especially 
in the shell-limestone, also in the tertiary mountains (Paris, 
Hohenhoven in Upper Swabia, etc.), and, when pure, it 
is usually applied to economical purposes, and to the arts. 
Alabaster is a finely granular variety, sometimes compact 
and translucent; it is distinguished from gypsum by its 
solidity and capability of polish, especially as it occurs in 
Tuscany and other Italian localities. 
Gypsum is characterised by its white or light colour, 
white streak, vitreous to pearly lustre, and slight hardness 
( = 2*0), and specific gravity (= 2*2—2*4). It is easily 
scratched by the nail of the finger. It is decomposed 
with difficulty, and is flexible in thin plates. The crys¬ 
tallised gypsum-spar or selenite can be split in the direc¬ 
tion of the rhomboidal planes ; in another direction it 
breaks, and in a third it bends, a behaviour common to no 
other minerals in equal masses. The chemical consti¬ 
tuents are simple sulphate of lime with two equivalents 
of water = 33”0 lime, 46‘0 sulphuric acid, and 21*0 
water (Ca S + 2 E). It is soluble in about 460 parts of 
water, and imparts to it an insipid, earthy, somewhat 
bitter taste ; the solution gives sulphuric acid and lime 
reactions. The waters of many springs which rise from 
gypsum rocks are quite saturated solutions of gypsum, 
and are therefore not quite sweet, and entirely unfit for 
the preparation of colours, beer, leather, etc., the more so 
on account of its not being separable by heat, as is the 
case with carbonate of lime. It is not at all, or almost 
imperceptibly, soluble in acids. Before the blow-pipe it 
melts, gives off water, reddens the flame, and is reduced 
to sulphuret of calcium ; the sulphur is usually, however, 
soon given off, and pure lime, which is easily recognised 
by its bright flame, remains. When melted along with 
fluor spar, it melts readily to a clear pearl, which grows 
dim on cooling. 
In the arts gypsum, when deprived of its water by 
burning at a slow red heat, and mixed with water, is used 
for casting statues, ornaments, and medals, and for friezes, 
chamber ornaments, the imitation of marbles, as stucco and 
mortar ; the gypsum containing lime, from the neighbour¬ 
hood of Paris, is frequently employed for the latter pur¬ 
pose, and is called plaster of Paris. 
The gypsum containing rock salt, the bituminous clay 
gypsum of the salt rocks, is used as a manure, especially 
in wet, damp soils, and for raising leguminous plants. 
Alabaster is made into statues, vases, time-pieces, and 
other works of art, especially in Tuscany. 
Figs. 11 and 12.— Anhydrite. 
The primary form is a right rectangular prism (Fig. 12), 
which may be split in all directions, but most easily in 
that of the lateral planes; truncations of the angles 
(Fig. 11), and of the lateral edges, are also found, as well 
as crystalline foliated granular masses, which have been 
called vulpinite, and in compact kidney-shaped masses, as 
tripe-stone. The colour is rarely pure white, more fre¬ 
quently reddish sky-blue or grey ; the transparency is very 
slight, the lustre between vitreous and pearly. The crys¬ 
tals are friable, the crystalline varieties very difficult to 
separate; hardness = 3'0—3"5, and specific gravity 
= 2"7—3*0, both being somewhat greater than in com¬ 
mon gypsum. In the matrass it gives off no water, but 
otherwise comports itself before the blow-pipe like gypsum. 
The elements are one equivalent of lime = 41 "53, and one 
equivalent of sulphuric acid = 58"47. Formula Ca S. The 
blue variety contains a small amount of iron, the grey is 
coloured by carbonaceous elements. When powdered and 
mixed with water, it gradually takes up two equivalents, 
and becomes changed into common gypsum. 
The anhydrite usually accompanies rock-salt at Bex, 
Wilhelmsgliick, Salz, etc. At the last-mentioned place 
fine sky-blue specimens are found in radiated granular, 
passing into foliated and compact masses, which take on a 
fine polish, and are used as marble. 
