Quantcast

The Mineral glaucophane

Silky Blaucophane Crystals

Glaucophane is named from a combination of the Greek words Glaukos, meaning "blue", and Phainelein, meaning "appearance", alluding to its bluish color. Glaucophane forms a series with the less-common Ferro-glaucophane, where Glaucophane is the magnesium-rich end member and Ferro-glaucophane is the iron-rich end member.

Chemical Formula

Na2Mg3Al2Si8O22(OH)2

Color

Blue, dark blue, and black with blue overtones

Crystal System

Monoclinic

Properties

Streak
Grayish blue
Hardness
5.5 - 6
Transparency
Translucent to opaque. Rarely transparent.
Specific Gravity
3.0 - 3.1
Luster
Vitreous, pearly
Cleavage
1,2
Fracture
Uneven, splintery
Tenacity
Brittle

Crystal Habits

Crystals are usually prismatic with a diamond-shaped cross-section. Often in platy groups of small prismatic crystals. Also bladed, columnar, acicular, fibrous, and massive. Crystals are often striated lengthwise.

Additional Information

Composition
Basic sodium magnesium aluminum silicate, often with some iron
In Group
Silicates; Inosilicates; Amphibole Group
Striking Features
Blue color, crystal and cleavage habits
Environment
In metamorphic schists and eclogites. Glaucophane is one of the components of blueschist rock, and is responsible for it bluish color.
Rock Type
Metamorphic

Varieties

 -   Iron-rich variant of Glaucophane, which has iron dominating over the magnesium in a solid solution series. Ferro-Glaucophane is recognized by the IMA as a distinct mineral species with the following chemical formula: Na2Mg3Al2Si8O22(OH)2. There can be iron replacing some of the magnesium up to 50 percent.
 -   Transparent to translucent variety of blue Glaucophane.

Noteworthy Localities

Glaucophane is more common than often perceived, though collector specimens of this mineral are seldom encountered, hence the few localities listed here. Groups of prismatic blue crystals come from Groix Island, Brittany, France; and transparent blue crystals from Rio Oremo, Chiavolino, Biella Province, Italy. In the U.S., Glaucophane is a constituent of the blueschist rocks throughout the Coast Ranges of Northern California, Oregon, and Washington. Dark blue crystals have been found in Ward Creek, Cazadero, Sonoma Co., California.

Distingushing Similar Minerals

Riebeckite - Usually darker in color.
Tourmaline - Harder, lacks good cleavage.

glaucophane Photos



Close

Copyright © 2021. Minerals.net

View on Full Site