from The American Heritage® Dictionary of the English Language, 4th Edition
- n. See plagioclase.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A plagioclase feldspar, the second member of the Albite-Anorthite solid solution series. Primarily found as small crystals in impure marble. Oligoclase contains a small amount of calcium substituting for some of the sodium in its formula. Oligoclase with reddish-golden inclusions found in Norway and Canada is called sunstone.
from the GNU version of the Collaborative International Dictionary of English
- n. A triclinic soda-lime feldspar. See feldspar.
from The Century Dictionary and Cyclopedia
- n. A soda-lime triclinic feldspar, the soda predominating. See feldspar.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. any of a series of triclinic feldspars that form rocks
It must be remembered, however, that it is only the orthoclase or potash felspars which contain large quantities of potash -- other felspathic rocks, such as oligoclase and labradorite, being comparatively poor in it.
There are, for instance, several different minerals commonly classified under the name of felspar, which have been distinguished by mineralogists by the names of orthoclase, albite, oligoclase, and labradorite; and there are at least two sorts of mica, two of hornblende, and many varieties of zeolites.
They are divisible into two great classes, which have received the names of diorite and dolerite, the former a mixture of albite and hornblende, the latter of augite and labradorite, sometimes with considerable quantities of a sort of oligoclase containing both soda and lime, and of different kinds of zeolitic minerals.
Dolerite, when composed entirely of augite and labradorite, produces rather inferior soils; but when it contains oligoclase and zeolites, and comes under the head of basalt, its disintegration is the source of soils remarkable for their fertility; for these latter substances undergoing rapid decomposition furnish the plants with abundant supplies of alkalies and lime, while the more slowly decomposing hornblende affords the necessary quantity of magnesia.
Aventurine felspar, known also as Sun-stone (_q. v._) is found principally at Tvedestrand in south Norway, and is a variety of oligoclase enclosing micaceous scales of haematite.
It depends on the felspar present -- _i. e._, whether it is orthoclase, oligoclase, or albite -- whether the soil will be rich in potash or not.
Day and his colleagues immediately recognized that these meteorites were unusual because of elevated contents of a light-colored feldspar mineral called oligoclase.
Perhaps 75\% of this is the plagioclase feldspars (mostly albite, oligoclase and labradorite) with the remainder as potassium feldspars (mostly microcline and orthoclase).