Oligoclase (from the Greek Greek ὀλίγος - small, insignificant and κλάσις - fracture) is a rock-forming mineral from the plagioclase subgroup of the feldspar group. It is an isomorphic mixture of 10-30% anorthite CaAl 2 Si 2 O 8 and 70-90% albite NaAlSi 3 O 8 .
| Oligoclase | |
|---|---|
 Oligoclase from India | |
| Formula | (Na, Ca) (Si, Al) 4 O 8 |
| Physical properties | |
| Colour | Brown, colorless, greenish, gray, yellowish |
| Trait color | White |
| Shine | Glass |
| Hardness | 6-6.5 |
| Density | 2.64 - 2.66 g / cm³ |
| Syngonia | Triclinic |