Oligoclase

n. (Mineralogy) feldspar mineral found in white crystals and at times shaded with red or gray or green

Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. In chemical composition and in its crystallographic and physical characters it is intermediate between albite (NaAlSi3O8) and anorthite (CaAl2Si2O8). The albite : anorthite molar ratio ranges from 90 : 10 to 70 : 30.Oligoclase is a high sodium feldspar crystallizing in the triclinic system. The Mohs hardness is 6 to 6.5 and the specific gravity is 2.64 to 2.66. The refractive indices are: nα=1.533 - 1.543, nβ=1.537 - 1.548, and nγ=1.542 - 1.552. In color it is usually white, with shades of grey, green or red.The name oligoclase was given by August Breithaupt in 1826 from the Greek oligos, little, and kasein, to break, because the mineral was thought to have a less perfect cleavage than albite. It had previously been recognized as a distinct species by J. J. Berzelius in 1824, and was named by him soda-spodumene (Natron-spodumen), because of its resemblance in appearance to spodumene.
See more at Wikipedia.org...

Noun
1. any of a rock-forming series of triclinic feldspars
(synonym) plagioclase
(hypernym) feldspar, felspar
(hyponym) albite, white feldspar
(substance-holonym) basalt

(n.)
A triclinic soda-lime feldspar. See Feldspar.
  

General Information:
 Chemical Formula:
(Na,Ca)(Si,Al)4O8
 Composition:
(Molecular Weight = 265.42 gm)
Sodium 6.93 % Na
Calcium 3.02 % Ca
Aluminum 12.20 % Al
Silicon 29.63 % Si
Oxygen 48.22 % O 
 Empirical Formula:
Na0.8Ca0.2Al1.2Si2.8O8
 Environment:
Magmatic and pegmatitic rocks.
 Locality:
Twedestrand, Norway.
 Name Origin:
From the Greek, oligos and kasein, "little cleavage."
Physical Properties:
 Cleavage:
[001] Perfect, [010] Good
 Color:
brown, colorless, greenish, gray, or yellowish.
 Density:
2.64 - 2.66, Average = 2.65
 Diaphaniety:
Transparent to Translucent
 Habits:
Euhedral Crystals - Occurs as well-formed crystals showing good external form., Granular - Generally occurs as anhedral to subhedral crystals in matrix.,
 Hardness:
7 - Quartz
 Luminescence:
Fluorescent.
 Luster:
Vitreous (Glassy)
 Streak:
white
More details...