Quick Reference

Silicate mineral (see silicates) and member of the chlorite group and particularly of the septichlorite group which also includes the minerals amesite, greenalite, and cronstedite; composition Fe2+10Al2[Si3AlO10]2(OH)16; soft but massive; occurs in sedimentary ironstones where it may form by alteration from the original siderite ore, and is found in association with chert and clay.

Subjects: Earth Sciences and Geography.

Reference entries