Hornstone—a very compact, silicious rock of horn-like texture, allied to flint; term also applied to flinty forms of felsite.
Hypogene rocks—those formed deep within the earth under the influence of heat and pressure.
Ironstone—a rock composed largely of iron, usually applied to clayey rocks having a large iron content.
Infusorial earth (tripolite)—an earthy or silt deposit consisting chiefly of the silicious shells of diatoms.
Itacolumite—a flexible sandstone whose pliability is due to an open arrangement of sand grains which are held together by scales of mica.
Jasper—a reddish variety of chalcedonic quartz.
Keratophyre—a felsite with a large percentage of soda.
Kersantite—a mica dolerite consisting chiefly of plagioclase, augite, and biotite.
Lapilli—small fragments of lava ejected from volcanoes; volcanic cinders.
Laterite—a red, porous, ferruginous residual earth of India and other tropical countries.