Igneous Rocks · common

Pegmatite

Pegmatite is an exceptionally coarse-grained igneous rock, typically granitic in composition, distinguished by crystals often several centimeters to meters in size, far larger than in ordinary granite. Its unusually large crystals result from crystallizing out of a water- and rare-element-enriched residual melt left over after most of a magma body has already solidified. Pegmatites serve as the primary source of many rare minerals and gemstones, including tourmaline, beryl, spodumene, and topaz.

Photo: No machine-readable author provided. Zimbres assumed (based on copyright claims). · Wikimedia Commons · CC BY-SA 2.5

Pegmatite properties at a glance

Type	Igneous Rocks
Mohs hardness	6–7
Luster	Vitreous (large crystal faces)
Fracture	Uneven to conchoidal
Specific gravity	2.6–2.8
Transparency	Opaque (individual crystals may be transparent)
Common colors	Pink, White, Gray, Multicolored (with tourmaline, etc.)
Rarity	common

Geology & background

Pegmatite forms during the final stages of granitic magma crystallization, when water, boron, fluorine, lithium, and other incompatible elements concentrate in the last remaining melt, lowering its viscosity and melting point and letting ions migrate freely enough to build unusually large crystals. This process often produces zoned bodies, with distinct mineral assemblages running from the outer wall zone to a central quartz core, plus pockets or vugs holding gem-quality crystals. Legendary pegmatite localities include Brazil's Minas Gerais, Afghanistan's Nuristan and Kunar provinces, California's Pala district, and Maine's Mount Mica, all famous for tourmaline, beryl, or other gem crystals.

Rockhounds specifically target pegmatites when hunting large, well-formed crystals of quartz, feldspar, mica, and a long list of rarer minerals like lepidolite, cassiterite, and columbite-tantalite, since pegmatites concentrate elements too scarce to form large crystals in ordinary rock. Because pockets can be unpredictable, systematic mining and collecting at a given deposit often follows mineralogical zoning patterns established from earlier finds. Safety matters too, since some pegmatites contain radioactive accessory minerals like uraninite or monazite that warrant caution while collecting.

How to identify Pegmatite

Pegmatite is identified primarily by its exceptionally large crystal size, often exceeding several centimeters, made up mainly of quartz, feldspar, and mica in a granite-like assemblage, with color and luster varying by the dominant minerals present. Hardness reflects its main constituents, generally around 6 to 7 for the feldspar and quartz. Fracture and cleavage likewise depend on which mineral within the rock is being examined. The coarse grain size alone usually distinguishes pegmatite from ordinary granite, which has much finer, more uniform crystals.

Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
Use multiple photos when possible, including a fresh surface and a close view of texture.

Where Pegmatite is found

Reported from multiple localities worldwide; verify locality against specimen provenance when available.

How much is Pegmatite worth?

Entry-level specimen	$1
Typical collector specimen	$10
Premium specimen	$75+

Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.

Common uses

Field identification
Construction or aggregate when suitable
Landscape interpretation
Education

Interesting facts

Pegmatites have produced some of the largest crystals ever documented, including single spodumene crystals from South Dakota measured in the tens of feet.
Many of the world's most famous colored gemstones, including tourmaline, morganite, and aquamarine, come almost exclusively from pegmatite pockets.
Pegmatites crystallize from the last, most chemically exotic dregs of a cooling magma, which is why they concentrate rare elements like lithium, beryllium, and tantalum.