158 A POPULAR EXPOSITION OF THE 
impart a red colour to rockets and signal lights, and for laboratory 
purposes. 
§ 5. INFUSIBLE. 
Zine Blende (Sulphide of Zinc) :—This mineral has been already 
described under sub-division B 3, (Vol. V. p. 182,) but it is men- 
tioned again in this place, as some of the light-coloured varieties 
present a vitreo-resinous or other non-metallic lustre. These are 
chiefly light brown or yellow, with colourless or very pale-brown 
streak. H. 3:°5-40. Infusible. Sometimes phosphorescent when 
rubbed or scratched. Small bright-yellow crystals and crystalline 
masses occur sparingly in cavities and fissures of the Niagara lime- 
stone in the vicinity of the Falls. For other localities, &c., see B 3, 
above. 
D 5. Streak, white. Yielding water in the bulb-tube. 
The minerals of this sub-division (many of which, however, are merely altered 
varieties of other species) may be conveniently grouped in three sections, as 
follows: § 1. YIELDING TRACKS ONLY, OR A VERY SMALL AMOUNT OF WATER: 
Mica, (some few varieties); Talc, (including Steatite); Renselaerite ; Diallage. 
§ 2. YIELDING A CONSIDERABLE AMOUNT OF WATER; SLOWLY DISSULVED BY BORAX 
BEFORE THE BLOWPIPE: Serpentine; Chlorite ; Loganite; Pholerite. $3. Yreup- 
ING A LARGE AMOUNT OF WATER: READILY DISSOLVED BY BORAX BEFORE THE BLOW- 
PIPE, THE BEAD, WHEN SATURATED, BECOMING OPAQUE: Gypsum. 
Mica :—In foliated masses, &c., with pearly pseudo-metallic lustre. 
Normally, anhydrous,—but specimens occasionally yield a little 
water when heated in the bulb-tube. See sub-divison D 4 (§ 1) 
above. 
Tale; (including Steatite );—Greenish-white, green, greyish, &c. 
In foliated, and also in compact masses, which feel more or less 
greasy, and which yield to the nail; sp. gr. 2°55-2°8. Very sectile. 
Flexible in thin foliz, but not elastic. Infusible. Composition : 
silica 62, magnesia 33, water 5. Talc occurs in the form of talcose 
slate, in foliated masses, and more especially in the form of steatite 
or compact tale, principally amongst the metamorphic rocks of the 
more modern series, south of the St. Lawrence. Under the latter 
condition, or that of steatite, it forms extensive beds in the town- 
ships of Potton, Sutton, Bolton, Stanstead, Leeds, Ireland, Broughton, 
&e., throughout this region. It occurs also, though far less abun- 
dantly, amongst the older metamorphic rocks of the Laurentian 
series, as in the townships of Marmora, Elzevir, &c., in Canada 
