tachylite - fragile basaltic glass from the 2018 Kilauea eruption that destroyed Kapoho, Hawaii - hand specimen

Tachylite is a lightweight and fragile basaltic volcanic glass, low in silica and with a pitchlike or resinous luster. In thin sections, tachylite is brown and translucent, with numerous crystals of magnetite.In Hawaii, entire lava flows can be tachylite, where the rapid cooling of basaltic flows has inhibited crystal formation. It rapidly weathers to palagonite, an orange to yellow isotropic mineraloid, forming a crust on lava flows, or simply crumbles as it weathers.  The term tachylite was first used by James Dwight Dana in 1868. Dana led the first geologic expedition to Hawaii in 1880-1881, followed by another look after Charles Dutton's 1884 Hawaii expedition. The publication of his observations in 1890 became the definitive source of information on Hawaiian volcanics for many years. Dana's Manual of Mineralogy, first published in 1848, became a much revised college text. My copy, the 1961 reprint of the 17th edition, revised by Harvard professor of mineralogy Cornelius Hurlbut J