88 Properties of Minerals. 
abraded or scratched with a knife or file are 
observed. The latter is called the Streak and the pow- 
der abraded the Streak Powder. The colors are either 
metallic or unmetallic. The metallic are named after 
some familiar metal, as copper red, bronze yellow, brass 
yellow, steel gray, lead gray, etc. 
The unmetallic colors used in characterizing min- 
erals are various shades of white, gray, black, blue. 
green, yellow, red and brown. 
FIFTH PROPERTY 
HARDNESS (WRITTEN H). 
To ascertain the comparative hardness of 
a mineral, it is only necessary to draw a file 
across the specimen or to make trials of scratch- 
ing one with another. As standards of comparison the 
following minerals have been selected, increasing grad- 
ually in hardness from talc, which is very soft, to the 
diamond, the hardest substance known. This table, 
called the scale of hardness, is as follows: 
Talc=1, Rock salt=2, Calcite=3, Flourite=4, Apa- 
tite=5, Orthoclase=6, Quartz=7, Topaz=8, Sapphire 
=9, Diamond=10. 
SIXTH PROPERTY. 
FRACTURE AND CLEAVAGE. | 
If a mineral has a poor cleavage and 
separates or breaks almost as readily in one 
direction as in another, smooth, curved surfaces 
often result. This kind of fracture is called 
conchoidal. Fracture is said to be uneven if on break- 
ing rough, irregular surfaces are exhibited, hackly when 
a jagged, irregular surface like that of broken cast iron 
results and splintery when the mineral breaks in splin- 
ters or needles. | 
