HUMITE

member of a group of layered silicate minerals related to the olivines that are nearly always restricted in occurrence to altered limestones and dolomites adjacent to acid or alkaline plutonic rocks and to skarns (contact-metamorphic rocks) near iron-ore deposits. The humite group includes norbergite, chondrodite, humite, and clinohumite. These yellow to brown, moderately hard minerals have a layered structure; the olivine mineral forsterite, magnesium silicate (Mg2SiO4), alternates with brucite, magnesium hydroxide , and differences in the physical properties and the crystallization result from differences in the stacking sequence. The humites rarely occur together in the same mass, but humite crystals have been found penetrated by clinohumite. For detailed physical properties, see olivine (table).