Pegmatite

Pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than 1 cm (0.4 in) and sometimes greater than 1 meter (3 ft). Most pegmatites composed of quartz, feldspar, and mica, having a similar silicic composition to granite. However, rarer intermediate composition and mafic pegmatites known.

Many of the world’s largest crystals found within pegmatites. These include crystals of microcline, quartz, mica, spodumene, beryl and tourmaline. Some individual crystals are over 10 m (33 ft) long.

The word pegmatite derives from Homeric Greek pegnymi, which means “to bind together”, in reference to the intertwined crystals of quartz and feldspar in the texture known as graphic granite.The term was first used by René Just Haüy in 1822 as a synonym for graphic granite. Wilhelm Karl Ritter von Haidinger first used the term in its present meaning in 1845.