Crystal Sphalerite

Chemical Formula

ZnS
The above is the formula of pure Sphalerite. However, since it usually occurs with some iron replacingthe zinc, its formula can be more accurately described as (Zn,Fe)S

Composition

Zinc sulfide, usually with some iron, sometimes with magnesium, manganese. In a few rare localities, it contains cadmium, indium, and gallium.

Variable Formula

(Zn,Fe)S ;
(Zn,Fe,Mg,Mn,Cd,In,Ga)S

Color

Black, brown, red, orange, yellow, green, gray. Rarely colorless. Some specimens contain crystals of different colors, and there is also a brown, globular, banded variety.

Streak

Pure Sphalerite has a white streak. However, impurities are almost always present, giving this mineral a light brown streak. The streak will always be a lighter color than the specimen.

Hardness

3.5 - 4

Crystal System

Isometric

Crystal Forms 
and Aggregates

Most commonly as tetrahedral crystals, which are usually twinned and grouped together. They may closely resemble octahedral crystals. Also occurs as groupings of distorted dodecahedral and cubiccrystals. Crystal faces are usually rounded or curved. May also be massive, grainy, botryoidal, stalactitic, and as large, distorted cleavage fragments.

Transparency

Transparent to opaque

Specific Gravity

3.9 - 4.1

Luster

Metallic, sub-metallic, adamantine, resinous

Cleavage

1,all sides, forming a dodecahedron

Fracture

Conchoidal

Tenacity

Brittle

Other ID Marks

1) Some transparent or translucent varieties fluoresce orange in shortwave ultraviolet light.
2) Commonly triboluminescent.

Complex Tests

Dissolves in hydrochloric acid, producing a sulfurous, rotten-egg odor

In Group

Sulfides; Simple Sulfides

Striking Features

Color and luster, crystal forms, and streak

Environment

In sedimentary limestone deposits, hypothermal veins and mesothermal veins, and in hydrothermalreplacement deposits. Occasionally in basalts.
 

Rock Type

Igneous, Sedimentary, Metamorphic

Popularity (1-4)

2

Prevalence (1-3)

1

Demand (1-3)

1