*« 
992 DESCRIPTIONS OF MINERALS. 
The name staurolite is from the Greek sfauwros, a cross. 
Schorlomite. Black, and often irised tarnished. Streak grayish-black. 
H.=7-7'5. G.=8 80. Fuses readily on charcoal. Easily decomposed 
by the acids, and gelatinizes. Contains much titanium, with iron, lime, 
and silica. From Magnet Cove, Arkansas, and Kaiserstuhlgebirge, 
Breisgau. 
B. HYDROUS SILICATES. 
The three sections under which the Hydrous Silicates 
are arranged are the following : 
I. GENERAL SECTION. Under this section there are in- 
cluded: (1) Sistlicates—Pectolite, Lanumontite, Apophy- 
lite, etc. ; (2) Unisilicates—Prehnite, Calamine, etc. ; and 
(3) Swbsilicates—as Allophane, and some related species. 
II. ZEOLITE SEcTION. The minerals included are feld- 
spar-like in constituents, and apparently so in quantivalent 
(or oxygen) ratio ; the basic elements being, as in the feld- 
spars, (1) aluminum, and (2) the metals of the alkalis K, 
Na, and of the alkaline earths Ca, Ba, with also Sr, to the 
almost total exclusion of magnesium and iron. 
Il]. MARGAROPHYLIITE SecTION. ‘This section em- 
braces species having a micaceous or thin-foliated struc- 
ture when crystallized, with the surface of the folia pearly, 
and the plane angle of the base of the prism 120°. Whether 
erystallized or massive the feel is greasy, at least when 
pulverized. It comprises (1) Bisilicates: including Tale and 
Pyrophyllite, which are atomically and physically similar 
species, although the former is a magnesium silicate, and 
the latter an aluminum silicate; (2) Non-alkaline Uni- 
silicates, including Kaolinite and Serpentine, which have a 
similar difference in constituents to the preceding with 

the same likeness in composition, and also some related | 
species ; (3) Alkaline Unisilicates : as, Pinite and the Hy- 
drous Micas, which are species containing potassium or | 
sodium as an essential constituent ; (4) the Chlorite Group, 
the species of which are mostly Subsilicates. 
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