The streak is the mark, made of fine powder, that a mineral leaves as
you rub it across a streak plate. A streak plate is a flat piece of
white tile or porcelain that has a dull, unglazed surface. The streak
plate is about as hard as quartz, which is _7_ on Mohs scale, and you
will not be able to use it for minerals that have a greater hardness.
For these, you can obtain the powder by scratching the mineral or by
crushing a small piece of it.
[Illustration: A streak plate is used to determine the color of the
streak or powder of a mineral.]
The color of the streak or powder is extremely helpful in identifying
some minerals. For example, hematite is a mineral that may be any one of
several different colors, but its streak or powder is always reddish
brown.