Crystal Smithsonite

Chemical Formula

ZnCO₃

Composition

Zinc carbonate, usually with some iron, magnesium, and calcium, occasionally with some cadmium, copper, and cobalt.
 

Variable Formula

(Zn,Fe,Mg,Ca,Cd,Cu,Co)CO₃

Color

Blue, green, yellow, yellow-green, orange-yellow, pink, purple, gray, brown, white, and colorless. May contain multicolored color zoning patterns and banding.

Streak

White

Hardness

4 - 5

Crystal System

Hexagonal

Crystal Forms 
and Aggregates

Mainly globular, botryoidal, stalactitic, and concretionary. Occasionally occurs as lenticular lumps, encrusting, massive, grainy, and as banded formations. Masses are sometimes porous. Crystals are rhombohedral and scalenohedral, and usually are rounded with curved faces. Crystals may contain triangular growth patterns.

Smithsonite is also known to form pseudomorphs of other minerals such as Calcite, Galena, and Fluorite, assuming the crystal shapes of those minerals.
 

Transparency

Translucent to nearly opaque

Specific Gravity

4.3 - 4.5

Luster

Vitreous, greasy, pearly, dull

Cleavage

1,3 - rhombohedral, usually curving

Fracture

Uneven, splintery. Conchoidal in individual crystals.

Tenacity

Brittle

Other ID Marks

1) May fluoresce pink in shortwave ultraviolet light.
2) Clear, transparent, rhombohedral crystals exhibit strong double refraction.

Complex Tests

Effervesces in hydrochloric acid

In Group

Carbonates; Calcite Group

Striking Features

High hardness for a carbonate and interesting crystal habits

Environment

As a secondary mineral formed from the alteration of primary zinc minerals in the oxidation zone.
 

Rock Type

Metamorphic

Popularity (1-4)

2

Prevalence (1-3)

2

Demand (1-3)

2