310 DESCRIPTIONS OF MINERALS. 
19:09=100°19. From Texas, Pa.; Webster, N. C.; Michipicoton 
Island, Lake Superior; Malaga, Spain ; Saasthal, Upper Valois. 
Kottisite is similar. 
Saponite. 
Soft, clay-like, of the consistence before drying of cheese 
or butter, but brittle when dry. Color white, yellowish, 
erayish-green, bluish, reddish. Does not adhere to the 
tongue. 
Composition. A hydrous silicate of magnesia containing 
some alumina. 
From Lizard’s Point, Cornwall, in serpentine. Also from 
geodes of datolite, Roaring Brook, Conn. ; in trap, north 
shore of Lake Superior. 
Kaolinite. 
Trimetric. ZA J=120°. Occurs massive, clay-like, but 
consisting usually of thin, microscopic, rhombic or hex- 
agonal, crystals ; either compact, friable, or mealy. 
~ Color white, orayish- white, yellowish, sometimes brown- 
ish, bluish, or reddish. Scales transparent or translucent ; 
flexible, inelastic, greasy to the touch. H.=1-2°5. Gs 
24-26. 
Composition. H,Al O,Si,+1aq=Silica 46°4, alumina 39°7, 
water 13:0=100. The similarity of the composition to that 
of serpentine will be seen on comparing the two formulas. 
B.B. infusible. A blue color with cobalt solution. Yields 
water in the closed tube. Insoluble in acids. 
Obs. The soapy feel of kaolinite distinguishes a clay con- 
sisting of it from other kinds of clay ; and when common 
clays are ‘‘ unctuous ” it is usually owing to the presence of 
kaolinite. Kaolinite has been made through the decompo- 
sition of aluminous minerals, and especially the potash and 
soda feldspars, orthoclase, albite, and oligoclase. In the 
case of these feldspars the process (1) removes the alkahes ; 
(2) leaves the alumina, or a large part of it, and part of the 
silica ; and (3) adds water. So that, with orthoclase, K,Al 
O,, 51, becomes changed to H,Al O,8i,+1 aq; half the water 
which is added replaces K, which is removed. Many gran- 
ites, gneisses, and other feldspar-bearing rocks tindergo 
r apidly this ch: ange, so that extensive beds ‘of kaolinite have 
been formed and are now making in many regions. The 
pao ee is usually washed out by streams or the waves from 
the decomposed material to make the large pure deposits. 
