Crystal Aegerine

Chemical Formula

NaFeSi₂O₆

Composition

Sodium iron silicate

Color

Black, brown, dark green, reddish black

Streak

Light gray

Hardness

6 - 6.5

Crystal System

Monoclinic

Crystal Forms 
and Aggregates

As long, thin, prismatic or bladed crystals, usually with a pointed pyramid on top (clinopinacoidal), and very often embedded in a matrix. Fibrous masses, radiating acicular sprays, and interlocking thin prismatic crystals are also common. May also be in reticulated masses and in grainy aggregates embedded in a matrix. Crystals are often striated lengthwise, and doubly terminated crystals are occasionally found.
 

Transparency

Opaque. Translucent in thin splinters.

Specific Gravity

3.5 - 3.6

Luster

Vitreous

Cleavage

1,2; Prismatic at cleavage angles of 87º and 93º (characteristic of minerals in the pyroxene group).
May also exhibit parting in one direction.

Fracture

Uneven, splintery

Tenacity

Brittle

In Group

Silicates; Inosilicates; Pyroxene Group

Striking Features

Unusually steep crystals and environment

Environment

An important mineral nepheline syenite pegmatites, also in metamorphosed schist and gneiss.

Popularity (1-4)

2

Prevalence (1-3)

3

Demand (1-3)

2