an all natural volcanic glass comparable to obsidian but having distinctive concentric cracks and a comparatively high water content. In a fluffy heat-expanded type perlite is employed as a lightweight aggregate, in fire-resistant insulation, plus in soil for potted flowers.
An amorphous volcanic glass formed because of the moisture of obsidian
The lightweight insulating material and aggregate caused by growing the cup by heat.
just like pearlite.
A peculiar kind of certain vitreous rocks, like obsidian and pitch-stone, the size of which often assumes the form of enamel-like globules.