How does pegmatite rocks form?

Being an igneous rock, a pegmatite can have numerous "origins". A pegmatite is thecoarsest of the igneous rock types, with the largest crystals, resulting from a very slow rate of cooling. At the Boomer Mine in the South Park of Colorado, a single beryl (beryllium aluminum silicate) crystal was mined from the pegmatite rock there which was six feet in diameter and nearly nine feet long. The Boomer Mine pegmatite is part of the Pikes Peak batholith. Unfortunately, it was uncovered on a weekend when the resident geologist was off work and the miners put the crystal into the mills crusher!! It should have gone to the Smithsonian Institute. You may know beryl as the semiprecious stone "aquamarine".