from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A dark-brown or dark-green to black mica, K(Mg,Fe)3(Al,Fe)Si3O10(OH)2, found in igneous and metamorphic rocks.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A dark brown mica; it is a mixed aluminosilicate and fluoride of potassium, magnesium and iron.
from the GNU version of the Collaborative International Dictionary of English
- n. Mica containing iron and magnesia, generally of a black or dark green color; -- a common constituent of crystalline rocks. See mica.
from The Century Dictionary and Cyclopedia
- n. An important member of the mica group of minerals. See mica.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. dark brown to black mica found in igneous and metamorphic rock
In certain minerals, notably the brown variety of mica known as biotite, the microscope reveals minute circular marks occurring here and there, quite irregularly.
Furthermore, their model included a second mineral called biotite, surrounding a zircon core.
And micas such as biotite have been found in regions containing evidence of the earliest life-forms, which are believed to have existed about 3.8 million years ago.
Cape Maclear at the north end is rocky, predominantly biotite-granite.
He also put a challenge to geologists to to synthesize "a hand-sized specimen of a typical biotite-bearing granite" as a test and was dismissed, G.
Vermiculite is formed by the alteration and/or weathering of the minerals biotite and phlogopite.
Black biotite contains potassium, iron, and magnesium.
The mica group of minerals includes: biotite, muscovite, lepidolite, and phlogopite.
The breakdown of biotite and phlogopite creates vermiculite.
Most significant is the presence of the Sinharaja Basic Zone, consisting of hornblende, pyriclasts, basic charnokites, pyroxene amphibolites and scapolite-bearing calc-granulites and blended with small amounts of quartzites, garnet-biotite gneisses and intermediate charnokites.