humite

from The Century Dictionary.

• noun Originally, a mineral from Vesuvius, occurring in small crystals yellow to brown in color, and belonging, as was believed, to three types of crystalline form.
• noun The relation in chemical composition of the species of the humite group is shown by the following formula, established by Penfield and Howe: chondrodite, Mg₃[Mg(F₁OH)]₂[SiO₄]₂; humite, Mg₅[Mg(F₁OH)]₂[SiO₄)₃; clinohumite, Mg₇[Mg(F₁OH))₂[SiO₄]₄. In these formulas the magnesium atoms present are, respectively, 5, 7, and 9, and these numbers also express the ratio of the vertical crystallographic axes of the three species. The fourth possible compound, Mg[Mg(F₁OH)]₂SiO₄. is probably represented by the species prolectite, which, though not yet analyzed, has been shown (Sjögren) to be crystallographically the first member of this series whose vertical axes are in ratio of 3:5:7:9. See prolectite.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Min.) A mineral of a transparent vitreous brown color, found in the ejected masses of Vesuvius. It is a silicate of iron and magnesia, containing fluorine.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun mineralogy An orthorhombic-dipyramidal mineral containing fluorine, hydrogen, iron, magnesium, oxygen, and silicon.