Crystals vary in size from 5mm – 20mm long
They are called “Pecos Diamonds” because they are only found in the Pecos River Valley, an area 20 miles wide and a north-south distance of about 100 miles, centering in Roswell, New Mexico and that when the sun’s rays are just right the desert looks as if it is just a sea of glittering diamonds. They were documented by Don Antonio de Espejo, a Spanish new world explorer, in 1583. Early cliff dwellers of the southwest area used them as drills and have also been used in ceremonial tools and for jewelry with the more recent Indians.
The great Capitan Barrier Reef grew 300 milllion years ago during the Permian time of the Paleozoic era, trapping the Permian Sea. When the sea evaporated it left beds of gypsum, know as the Permian-Whitehorse formation. Quartz crystals formed in the gypsum. Then over time and natural erosion they have been released. Pecos diamonds are doubly terminated hexagonal prisms and although quartz replacing gypsum is not unusual, the development of such doubly terminated crystals by its replacement is. The crystals are usually small, most under an inch, are semi-transparent, but the majority are translucent to opaque. They vary from clear to white, pink, yellow, orange, red, green, brown, and black shades.