Crystal Chalcedony

Chemical Formula

SiO₂

Composition

Silicon dioxide

Color

White, blue, red, green, yellow, orange, brown, pink, purple, gray, black, colorless, and multicolored. Often banded in many different color combinations, and a few rarer forms are iridescent.

Streak

White

Hardness

7

Crystal System

Hexagonal

Crystal Forms 
and Aggregates

Chalcedony, being a microcrystalline variety of the mineral Quartz, does not occur in visible crystals. It occurs in botryoidal, mammilary, stalactitic, massive, nodular forms, as smooth rounded pebbles, asbanded masses, as amygdules, and as the linings of geodes.

Transparency

Transparent to opaque

Specific Gravity

2.6 - 2.7

Luster

Vitreous, waxy, or dull

Cleavage

None

Fracture

Conchoidal

Tenacity

Brittle

Other ID Marks

1) Commonly fluorescent, usually green or white.
2) Triboluminescent
3) Piezoelectric

Complex Tests

Dissolves in hydrofluoric acid

In Group

Silicates; Tectosilicates; Silica Group

Striking Features

Hardness and form

Environment

Occurs in all mineral environments, especially in igneous environments.
 

Rock Type

Igneous, Sedimentary, Metamorphic

Popularity (1-4)

1

Prevalence (1-3)

1

Demand (1-3)

1