Perlite (fr. perlite, from perle - pearl) is a rock of volcanic origin.
At the edge of the lava flow, in the places of primary contact of magmatic melts and the earth surface, as a result of rapid cooling (quenching) of the lava, volcanic glass - obsidian is formed. Subsequently, under the influence of groundwater, it is hydrated and, as a result, perlite is formed.
Perlite is characterized by a fine concentric-skinned separateness (perlite structure), along which it breaks up into rounded nuclei (pearls), resembling pearls with a characteristic luster. Among other volcanic rocks, perlite is distinguished by the presence of constitutive water (more than 1%). The porosity may be 8-40%.
Perlite may have black, green, red-brown, brown and white color of different tones. Perlite varieties: obsidian (with obsidian admixtures), sherulitic (with feldspar admixtures), resinstone (homogeneous in composition), glassy and others.
According to the textural features, massive, banded, breccia, and pumice perlite are distinguished.
