Chalcedony

Real mineral · common · SiO₂

A cryptocrystalline variety of silica with fibrous internal structure invisible to the naked eye. Encompasses agate, jasper, onyx, and chrysoprase. Forms in vesicles of volcanic rocks and in low-temperature hydrothermal environments.

Identity

Formula

SiO₂

Chemical class

silicate

Mineral group

Amethyst, Bloodstone, Carnelian, Citrine, Quartz, Rose Quartz, Smoky Quartz, Tiger's Eye

Also known as

Agate (banded), Jasper (opaque), Onyx (layered black-white), Chrysoprase (green)

Crystallography

Crystal system

trigonal

Habits

massive, botryoidal, stalactitic, nodular

Fracture

conchoidal

Physical properties

Mohs hardness

7

Density

2.6 g/cm³

Luster

waxy, vitreous

Colors

white, gray, blue, red, brown, green, yellow, multicolored

Streak

white

Transparency

translucent, opaque

Geology

Origins

hydrothermal, sedimentary, volcanic

Host rocks

basalt, limestone, rhyolite

Associated minerals

Quartz, Opal, Calcite

Geography

worldwide

Classification

Rarity

common

Gem quality

Yes

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