|
Nosean
|
|
Property
|
Value
|
| Formula |
Na8(Al6Si6O24)SO4 |
| Mineral Group |
Feldspathoid: Sodalite Group |
| Crystal System |
Isometric (Cubic) - Hextetrahedral |
| Crystal Habit |
Dodecahedral, or elongate pseudohexagonal prisms |
| Cleavage |
(110) Poor |
| Color/Pleochroism |
Colorless, gray, or very pale blue in thin section
or grain mount |
| Optic Sign |
Isotropic |
| 2V |
N/A |
| Optic Orientation |
N/A |
|
Refractive Indices
n =
|
1.470-1.495 |
| Max Birefringence |
N/A |
| Elongation |
None |
| Extinction |
None |
| Dispersion |
None |
| Hardness |
5.5 - 6.0 |
| Specific Gravity |
2.3 - 2.4 |
| Streak |
White to bluish-white |
| Luster |
Vitreous |
| Distinguishing Features |
Has moderate negative relief. It may not be possible to
distinguish between the members of the Sodalite mineral group based on
their optics. However, Sodalite is usually colorless, lacks abundant inclusions,
and is the only one found in plutonic rocks; nosean and hauyne commonly
contain dark inclusions that may be concentrated into sectors, planes,
cores, or rims. Both nosean and hauyne are commonly blue in thin
section. |
| Occurrence |
The Sodalite group is found in silica-deficient alkalic
igneous rocks. Nosean is generally restricted to volcanic rocks. The volcanic
rocks that the sodalite group is found in include phonolites, alkali basalts,
trachyte, and feldspathoidal basalt. The commonly associated minerals are
nepheline, leucite, and sanidine. |
| Editors |
Julie Herrick ('02), Meaghan Moy ('03), and Vanessa O'Connor ('05) |
