Tripoli

Tripoli (Diatomite), a mineral substance employed in polishing metals, marble, glass, &c., so named because it was originally brought from Tripoli in Africa. It is a siliceous rock, composed of the siliceous frustules of Diatomaceæ. It is frequently soft, friable, and earthy, but now and then is rendered firmer and more solid, and even extremely hard, probably from impregnation with opal substance. The more dust-like varieties are called Kieselguhr, and are in much demand for the manufacture of Dynamite (q.v.). Kieselguhr has been met with in alluvial (generally lacustrine) deposits in many countries. It occurs in beds underneath peat in Britain, Norway, Germany, &c. Diatomaceous deposits are forming at the present day both in fresh water and in the sea: those which are worked for economic purposes ranging in age from Tertiary to recent times. Ehrenberg estimated that every cubic inch of Bilu Tripoli weighing 220 grains contained 41,000,000,000 of these minute water-weeds.