A perlite is an obsidian, or other vitreous rock with a concentric structure and which is expansible by heating. A rhyolitic glass with abundant spherical or convolute cracks that cause it to break into small pearllike masses or pebbles, usually less than a centimeter across; it is commonly gray or green with a pearly luster and has the composition of rhyolite. Also known as pearlite; pearlstone.
No related terms.