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Earth and Space > Rock Identification (table)

The tables below may help the quick identification of an unknown rock type. These tables can be used alongside our Rock Identification Key to identify rarer rocks that aren’t included amongst the photographs on that page.

The tables are split into Sedimentary, Metamorphic and Igneous types.


Hardness Grain Size Composition Other Rock Type
hard coarse clean quartz white to brown Sandstone
hard coarse quartz and feldspar usually very coarse Arkose
hard or soft mixed mixed sediment with rock grains and clay grey or dark and "dirty" Wacke/
hard or soft mixed mixed rocks and sediment round rocks in finer sediment matrix Conglomerate
hard or
mixed mixed rocks and sediment sharp pieces in finer sediment matrix Breccia
hard fine very fine sand; no clay feels gritty on teeth Siltstone
hard fine chalcedony no fizzing with acid Chert
soft fine clay minerals foliated Shale
soft fine carbon black; burns with tarry smoke Coal
soft fine calcite fizzes with acid Limestone
soft coarse or fine dolomite no fizzing with acid unless powdered Dolomite rock
soft coarse fossil shells mostly pieces Coquina
very soft coarse halite salt taste Rock Salt
very soft coarse gypsum white, tan or pink Rock Gypsum


Foliation Grain Size Hardness Usual Colour Other Rock Type
foliated fine soft dark "tink" when struck Slate
foliated fine soft dark shiny; crinkly foliation Phyllite
foliated coarse hard mixed dark and light wrinkled foliation; often has large crystals Schist
foliated coarse hard mixed banded Gneiss
foliated coarse hard mixed distorted "melted" layers Migmatite
foliated coarse hard dark mostly hornblende Amphibolite
nonfoliated fine soft greenish shiny, mottled surface Serpentinite
nonfoliated fine or coarse hard dark dull and opaque colours, found near intrusions Hornfels
nonfoliated coarse hard red and green dense; garnet and pyroxene Eclogite
nonfoliated coarse soft light calcite or dolomite by the acid test Marble
nonfoliated coarse hard light quartz (no fizzing with acid) Quartzite


Grain Size Usual Colour Other Composition Rock Type
fine dark glassy appearance lava glass Obsidian
fine light many small bubbles lava froth from sticky lava Pumice
fine dark many large bubbles lava froth from fluid lava Scoria
fine or mixed light contains quartz high-silica lava Felsite
fine or mixed medium between felsite and basalt medium-silica lava Andesite
fine or mixed dark has no quartz low-silica lava Basalt
mixed any colour large grains in fine-grained matrix large grains of feldspar, quartz, pyroxene or olivine Porphyry
coarse light wide range of colour and grain size feldspar and quartz with minor mica, amphibole or pyroxene Granite
coarse light like granite but without quartz feldspar with minor mica, amphibole or pyroxene Syenite
coarse medium to dark little or no quartz low-calcium plagioclase and dark minerals Diorite
coarse medium to dark no quartz; may have olivine high-calcium plagioclase and dark minerals Gabbro
coarse dark dense; always has olivine olivine with amphibole and/or pyroxene Peridotite
coarse dark dense mostly pyroxene with olivine and amphibole Pyroxenite
coarse green dense at least 90% olivine Dunite
very coarse any colour usually in small intrusive bodies typically granitic Pegmatite

Related Links

Rock Identification Key

Rock Types