Earths, 
Earths. M I rN E R A L O G Y, 
44 <-> 
Magnesiata. See that article, vol.xiv.— Profeffor Kidd 
obferved, that magnefia had not been met with m a na¬ 
tive it a te: it has, however, been found native m New 
Terfev, North America, in the year 1810. _ 
Sir Humphry Davy has afcertained by experiment, that, 
by mixing twenty or thirty grains of common magnelia 
with each pound of the worlt flour, it will make biead ot 
the belt quality. 
Gypsum. See that article, vol. ix:— Generic charac¬ 
ters: Coniifting ofcarbonat of lime united to fulphuric 
acid : light, very foft, a little frigid : not commonly effer- 
vefcmg with nitric acid, melting with difficulty in the 
fire, but eafily crumbling to powder, which caufes no 
ebullition in water, but forms a pafte hardening and dil- 
tending by expol'ure to the air. 
Plotter of Paris is prepared from gypfum by calcina¬ 
tion: which procefs drives oft the water of the fulphat ot 
lime, and the carbonic acid or fixed air of the carbonat 
of lime, contained originally in the gypfum. The gyp¬ 
fum in this ftate has a ftrong difpofition to abforb a cer¬ 
tain proportion of water; and during this abforption the 
mafs is confolidated : in which procefs it is luppofed that 
the particles of the calcined carbonat of lime aft as a 
connecting medium round which the fulphat of lime, iiy 
re-combining with the water that had been driven off 
during the calcination, undergoes a hafty and imperfeCt 
cryftallization. There are eighteen fpecies, belides fe- 
reral varieties. 
1. Gypfum terreum, or earthy gypfum : powdery, of a 
white colour. Found in the fifiures of gypleous rocks in 
Saxony, in the form of a white friable loofe powdery fub- 
ftance, and feems to originate from cryftallized felenite, 
and will not concrete without being wetted: feels dry 
and meagre, hardly finks in water, is not gritty between 
the teeth; when heated below rednefs, it becomes of a 
dazzling white: has no luftre or tranfparency. 
a. Gypfum arenaceum, or fandy gypfum : confifting of 
white diftinft fubdiaphanous granulations. Found in 
Thuringia, and originates from alabaiter which lias crum¬ 
bled to powder: it refembles the laft, except that its par¬ 
ticles are larger, like unto fmall grains of fluid, and are 
very gritty between the teeth. 
3. Gypfum alabaftrum, compaCt gypfum, or alabafter: 
compaCt:, dry, and meagre; a little Alining, breaking 
into indeterminate fragments of a common form, receiv¬ 
in' 3- a polifn. Found in Derbyfhire, Perfia, and various 
parts of Ruffia, Spain, Tufcany, Sicily, and other places, 
in flratified mountains. Colour various, fometimesfpotted, 
interfeCted with veins, and depicted with various colours : 
does not effervefce with acids, when pure, is fofter than 
marble, and does not take a good polilh: texture Ihivery 
and glittering. Contains carbonat of lime 32, fulphuric 
acid 30, water 38. Specific gravity, 1-872 to 2-288. 
Alabafter, from its beauty and the facility with which 
■it can be worked, is ufed for ornamental architecture and 
fculpture; but the folubility of this ftone renders it ill- 
fuited to relift the agency of weather. Dr. Watfon re¬ 
lates, that he fufpended two ounces of this ftone in a 
pail of water forty-eight hours, changing the water feve- 
ral times; and found that it had loft one-thirtieth part 
of its weight. This alabafter was perhaps one of the 
fofteft kind; but the experiment may ferve to fliow that 
this ftone will not bear expofure to rain. 
The ancients have mentioned a beautiful fpecies or va¬ 
riety of alabafter, which they call pliengites. It was a very 
rude and irregular mafs, very fliattery and friable, yet of 
a brightnels fuperior to that of moll of the other marbles, 
and excelling them all in tranfparence; in colour of an 
agreeable pale yellowilh, white, or honey-colour ; the yel¬ 
low more intenfe in lome places than in others, and lome- 
times making an obfcure relemblance of veins. The an¬ 
cients were very fond of this in their public buildings ; 
and the Temple of Fortune, built wholly of it, has long 
been famous. Its great beauty is its tranfparence, from 
Vol. XV. No. 1056. 
which alone this temple was perfectly light when the 
doors were (hut, though it was built without a window, 
and had no other light but what was tranfmitted through 
the ftone its walls were built with. It was anciently 
found in Cappadocia, and is frill plentiful there : we have 
it alfo in Germany and France, and in our own kingdom 
in Derbyffiire, and lome other counties. It takes an ex¬ 
cellent polilh; and is very fit for ornamental works, where 
there is no great; ftrength required. The above we copy 
from Hill’s Hilt, of Foffils, p. 4.90. but it mull be obferved, 
that, from a paflage Suetonius, pliengites feems applicable 
not l’o much to a tranfparent marble as to one that is 
opaque, and capable of reflecting the rays of light like a 
mirror. The palfage alluded to is in the life of Domitian : 
“Parities phengite lapide dijlinxit; e enjus Jplendore per 
imagines quicqitid a tergo jieret providcret ; Fearful of being 
affalfinated, he lined, in various places, the walls of the 
portico where he ufed to walk with the ftone called phen- 
gites, by the reflection of which he could fee every object 
behind him.” Suet, in Dom. cap. xiv. 
4. -Gypfum fibrofum, or fibrous gypfum: meagre and 
dry, brittle, breaking into long fplintery fragments, of a 
common form. There are two varieties : a. Very tranf¬ 
parent, fixed, united. [ 3 . Obfcure, fixed, with deculflite 
ramentations. Both are found in various parts of Britain 
and Europe; and, according to Mr. Sowerby, formed by the 
decompolition of fulphur of iron, or pyrites, the fuiphur 
of which combining with oxygen forms fulphuric acid, 
which, coming in contact with lime, forms this gypfum in 
various fanciful modes. Its texture is fibrous, filamen¬ 
tous, or radiate, flexuous or ltraight, parallel or (battered ; 
colour white, grey, yellowilh, red, or honey-colour, with 
the colours fometimes meeting in ftripes. 
5. Gypfum fchiftofum, or Ihiftofe gypfum : meagre and. 
dry, breaking into indeterminate fragments, fibrolo-la- 
mellous, with Ihort fibres cutting the foliations perpen¬ 
dicularly. Found in Tufcany and Wirtemberg ; white. 
6. Gypfum radiatum, or radiated gypfum : meagre and 
dry, radiate in a parallel manner, breaking into indeter¬ 
minate fragments. Found near Coburg in the province 
of Mansfield : the rays fometimes broader, fometimes nar¬ 
rower. 
7. Gypfum ufuale, or common gypfum : meagre and 
dry, lamellar, with the foliations generally fpherical; 
breaking into indeterminate fragments. There are two 
varieties : a. Shining internally ; 13 . Without luftre in¬ 
ternally. Gypfum is found in Britain and various parts 
of Europe, and in Nova Scotia and New Brunfwick in 
Britilh America, in vaft maffes, and fometimes in lenticu¬ 
lar cryftals. Colouryellovvilh or blackilh-grey, cinereous, 
ochraceouSjflelh-colour, rarely honey-colour. Breaks into 
fine and coarle grained concretions, fometimes cohering 
fo loofely as to be ealily triturated between the fingers. 
8. Gypfum lamellare, or lamellated gypfum : Aiming, 
breaking into indeterminate pieces, of a common form, 
lamellar with the foliations incurved. Found in Thurin¬ 
gia, Wirtemburg, and Spain. Diaphanous or opake, 
iinoke-colour, white, or yellowifli. 
9. Gyplum fpeculare, or lamellar-pellucid gypfum ; 
pellucid, white, Aiming, of a common form ; breaking 
into rhomboidal lpecular fragments ; lamellar with ltraight 
foliations. Found, amorphous or cryftallized, in various 
mountains of Europe, generally in the vicinity of lalt 
lakes and pits : the thinner foliations are a iittle fonorous 
and very fine : the cryftals are in iix-lided prifms termi¬ 
nating in an edge, or rliomboidal, wedge-form, tubular 
or lenticular; the planes of the cryftals which form the 
acute angles are ftreaked longitudinally, thofe that form 
.the obtule are fmootli. 
10. Gyplum glaciale, or icy gypfum : pellucid, white. 
Alining, of a common form, breaking into wedge-form 
fragments, lamellar with ltraight parallel foliations. 
Found with the laft fpecies, of which it may probably be 
only a variety. 
11. Gypfum felenites, or felenite: pellucid, Alining, 
5 Y rhombic-. 
