igneous
Quartz-rich pegmatite with mica and dark inclusions
Pegmatite; chiefly quartz (SiO₂), with feldspar and biotite/tourmaline inclusions
AI-generated identification · may be incorrectCoarse-grained, white to translucent quartz with vitreous to pearly luster and irregular fracture; quartz hardness is Mohs 7, while feldspar is about 6 and biotite 2.5–3. Visible dark flakes or masses are likely biotite mica or schorl tourmaline; exact identification requires testing.
Identified More igneous →
Explore Quartz-rich pegmatite with mica and dark inclusions in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Coarse-grained, white to translucent quartz with vitreous to pearly luster and irregular fracture; quartz hardness is Mohs 7, while feldspar is about 6 and biotite 2.5–3. Visible dark flakes or masses are likely biotite mica or schorl tourmaline; exact identification requires testing.
Formation & geological history
Formed when water-rich granitic magma cooled slowly in a late-stage intrusion, allowing exceptionally large crystals to grow. Most pegmatites are Precambrian to Mesozoic, though their age depends on locality.
Uses & applications
Used as a source of quartz, feldspar, mica, and occasionally lithium, beryllium, tantalum, or gem minerals; attractive pieces are collected as mineral specimens. This irregular fragment has modest commercial value.
Geological facts
Pegmatites are famous for producing giant crystals and gemstones such as tourmaline, beryl, and spodumene. The specimen’s white material may be quartz, feldspar, or both; acid and hardness tests can help distinguish them.
Field identification & locations
Common in granitic terrains worldwide, including Brazil, the United States, Madagascar, and Scandinavia. Look for very coarse crystals, mica sheets, and sharp mineral contacts; estimated value is about $5–$30, or $50+ if the dark inclusion proves to be a desirable mineral.
