very coarse grained plutonic rock

A pegmatite is an igneous rock with a very rough texture, which has large interlocking crystals[1] that are usually bigger than 1 centimeter (0.4 in) and sometimes bigger than 1 meter (3 ft).[2]

Pegmatite with blue corundum crystals

Many of the world's largest crystals are found in pegmatites. These include crystals of quartz, mica, beryl, and tourmaline. Some of these crystals are over 10 m (33 ft) long.[3]


The word pegmatite comes from the Homeric Greek word, πήγνυμι (pēgnymi), which means “to bind together." This refers to the interlocked crystals in the rock's texture.[4]


  1. Jackson, Julia A., ed. (1997). "Pegmatite". Glossary of Geology (4th ed.). Alexandria, Viriginia: American Geological Institute. ISBN 0922152349.
  2. Blatt, Harvey; Tracy, Robert J. (1996). Petrology: Igneous, Sedimentary, and Metamorphic (2nd ed.). New York: W.H. Freeman. p. 73. ISBN 0716724383.
  3. Schwartz, G. (1928). "The Black Hills Mineral Region". American Mineralogist. 13: 56–63.
  4. London, David; Morgan, George B. (2012-08-01). "The Pegmatite Puzzle". Elements. 8 (4): 263–68. doi:10.2113/gselements.8.4.263. ISSN 1811-5209.