M917 - Perlite Specimen (Utah).

Perlite is a natural volcanic glass, similar to obsidian, but having
distinctive concentric cracks and relatively high water content. It
is made up of about 75% silicon dioxide (quartz) and about 15%
aluminum oxide. Perlite has many uses; as an insulation and in soil
for potted plants are among the primary uses. Not a pretty stone,
but very interesting material. Porous and rough looking material.
Good price though!

From  Utah.

Price:   $ 1.95 each