"Freeze-Dried Specimens"

Dark gray with abundant gas pocket vesicles.

Volcanic glass with snowflakes embedded throughout.

Pale pink felsite, with small sanidine phenocrysts.

Red-brown to gray, coarse-grained, containing feldspar and mica.

Silvery, paragranite and muscovite-rich with medium garnet crystals.

Black, soft; most widely mined.

Lustrous, black 'hard coal'.

Light gray, fine small clasts.

Dense and massive.

Hematite-cemented quartz; orthoquartzite.