sinter

In mineralogy, calcarious sinter is a variety of carbonate of lime, composed of a series of successive layers, concentric, plane or undulated, and nearly or quite parallel. It appears under various forms. Silicious sinter is white or grayish, light, brittle, porous, and of a fibrous texture. Opaline silicious sinter somewhat resembles opal. It is whitish, with brownish, blackish or bluish spots, and its fragments present dendritic appearances. Pearl sinter or fiorite occurs in stalactitic, cylindrical, botryoidal, and globular masses, white or grayish.