Identification of rocks and minerals

If white and colorless and…

Aragonite – coarse, glassy needle-like crystals with striated (grooved) sides and angular tips

Calcite – abundant, soft, blocky masses or steeply pointed six-sided crystals within cavities in rock

Cowlesite – tiny ball-like masses, often intergrown with each other, found very rarely within cavities in basalt

Feldspar – blocky, angular opaque crystals or dull light-colored masses within coarse-grained rocks, like granite

Mesolite – very delicate, flexible, hair-like crystals grown in tangled masses within cavities in basalt

Opal – glassy opaque masses with no particular crystal shape, found filling cavities in rock; silica, resemble glass, no organized structure (mineraloid), form massively, translucent glass blobs, fill cavities in rock or thundereggs, embedded in host stone, opalescent (a form of iridescence-changes color as the angle changes)

Quartz – common light-colored masses, pebbles or six-sided pointed crystals that are very hard

If gray and…

Barite – blocky, wedge-shaped crystals that feel very heavy for their size

Basalt – abundant dark rock with a very fine grain size, often containing many round bubble-like cavities

Chalcedony – very hard, translucent material that can’t be scratched with a knife, often found on beaches

Chert – dense, very hard, opaque rock that can’t be scratched with a knife, often found on beaches

Limestone – soft rock that fizzes in vinegar and is easily scratched with a knife

Mica group – shiny, nearly metallic, flexible and soft crystals or masses within rock

Quartzite – very hard rock that resembles quartz but has a grainy texture, often found on beaches

Rhyolite – light-colored, fairly hard rock abundant in the Cascade Mountains, often containing many gas bubbles

Shale or slate – rocks consisting of many thin, flat, parallel layers that can often be separated with a knife

Talc or soapstone – very soft masses of flaky crystals with a very “slippery” feel

If black and…

Manganese oxides – dusty coatings or veins within rocks and minerals that often darken your hands

Obsidian – dense, hard material that resembles black glass

Pyroxene group – dark and glassy, blocky crystals within rocks, particularly dark rocks like gabbro

If blue and…

Chrysocolla – soft, crumbly masses with no particular shape, often alongside malachite

Opal – glass-like masses with no particular shape found filling cavities in rock

If green and…

Epidote – very hard pea-green elongated crystals with striated (grooved) sides

Flourite – rare glassy masses exhibiting angular, blocky surfaces and internal cracks

Garnet group – very hard glassy crystals resembling faceted balls, often embedded within quartz or schist

Jade – masses of dense translucent material primarily found on beaches

Malachite – vividly colored botryoidal (grape-like) crusts or masses, or rare delicate needle-like crystals

If brown and…

Barite – blocky, angular crystals that feel very heavy for their size

Chalcedony – dense, very hard material unable to be scratched with a knife, often found on beaches


Clay minerals

Feldspar Group

Fossils, animal

Fossils, plant

Garnet group



Mudstone or siltstone





Volcanic bombs

If red and…


Garnet group



If orange and…

Agate, carnelian


If violet or pink and…

Agate, color variations

Quartz, varieties


If metallic and…







If multicolored or banded and… then try…

Agate – concentric banding and translucency

Agate, gravitationally banded

Agate, moss – very hard translucent masses containing moss-like tangles of colored material within

Agate, plume – very hard translucent masses containing feather- or smoke-like growths of material within

Agate, sagenitic

Agate, thunder eggs

Agate, tube

Conglomerate or breccia


Gneiss or schist


Jasper – opaque, conchoidal fracture, red-orange, brown-yellow or green

Jasper, fancy – colored stripes, streaks, curving layers, orbs

Jasper, picture

Petrified wood




Volcanic rocks