Pegmatite

A pegmatite is an igneous rock with a very rough texture, which has large interlocking crystals that are usually bigger than  and sometimes bigger than .

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  long.

Etymology
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.

References

Category:Igneous rocks