Ro DESCRIPTIONS OF MINERALS. 
also coarse and fine granular; also compact, either amor- 
phous, or presenting stalactitic and mammillary shapes. 
Crystals often as pellucid as glass, and colorless ; some- 
times topaz-yellow, amethystine, rose, smoky, or other tints. 
Also of all degrees of transparency to opaque, and of various 
shades of yellow, red, green, blue and brown colors to black. 
In some varieties the colors are in bands, stripes, or clouds, 
Blas i5 (Cp Seo 
Ve 2. 3 4, 
5. 

Composition. Si0,=Oxygen 53°33, silicon 46°67=100. 
Opaque varieties often contain oxide of iron, clay, chlorite, 
or some other mineral disseminated through them. B.B. 
infusible. With soda, fuses with effervescence. 
Diff. Quartz is exceedingly various in color and form, 
but may be distinguished, by (1) absence of true cleavage ; 
(2) its hardness; (38) its infusibility before the blowpipe ; 
(4) its insolubility with either of the common acids; (8) its 
effervescence when heated B.B. with soda; and (6) when 
crystallized, by the forms of its crystals, which are almost 
always six-sided prisms terminating in six-sided pyramids. 
The varieties of quartz owe their pecularities either to 
erystallization, mode of formation, or impurities, and they 
fall naturally into three series. 
I. The vitreous varieties, distinguished by their glassy 
fracture. 
II. The chaleedonie varieties, having a subyitreous or a 
waxy lustre, and generally translucent. | 
Il]. The jaspery cryptocrystalline varieties, having barely 
a glimmering lustre or none, and opaque. 
I. VITREOUS VARIETIES. 
tock Crystal. Pure pellucid quartz. , 
This is the mineral to which the word erystal was first 
apphed by the ancients ; it is derived from the Greek krus- 
tullos, meaning ice. The pure specimens are often cut and 
used in jewelry, under the name of ‘* white stone.” 
It is often used for optical instruments and spectacle 

