Some minerals allow light to pass through them; others do not. A mineral
is _transparent_ if you can see both light and objects through it, as
through clear glass. If you can see only light, but no objects, as
through frosted glass, the mineral is _translucent_. When you hold an
_opaque_ mineral up to the light, it looks dark. No light at all comes
through it, even through the thin edges.
[Illustration: Transparent mineral.]