| Definitions | | nepheline |
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noun
- (mineralogy) A feldspathoid mineral of silica-poor igneous, plutonic and volcanic rocks. Chemically, Nepheline is a plagioclase feldspar with insufficient silica to satisfy the chemical bonds. Because of the unfilled bonds, Nepheline weathers rapidly and can only be seen as inclusions in freshly broken rock.
- Chemical composition: Sodium potassium aluminum subsilicate, <math>(Na,K)(Al,Si)_2O_4</math>
- Physical properties:
Moh's Hardness: 5.5-6.0
Specific gravity: 2.5-2.6
Color: Colorless, white, gray, reddish, smoky; transparent to translucent
Fracture: Subconchoidal
Cleavage: Good prismatic
Habit: Hexagonal-Hexagonal pyramidal
- Fluorescence: Often orange-red in portions of crystals
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