"A variety of quartz which is peculiar in consisting of bands or layers of various colors blended together."-Whitney, 1902

Agate

"A variety of quartz which is peculiar in consisting of bands or layers of various colors blended together."-Whitney,…

"Outcrop showing faults, spur south of Deadwood." -Walcott, 1901

Outcrop

"Outcrop showing faults, spur south of Deadwood." -Walcott, 1901

"Determination of the optical character of a uniaxial crystal with the gypsum plate. Quartz (+)." -Johannsen, 1908

Gypsum Plate

"Determination of the optical character of a uniaxial crystal with the gypsum plate. Quartz (+)." -Johannsen,…

"Determination of the optical character of a uniaxial crystal with the gypsum plate when the center of the cross is beyond the field of the microscope. Quartz (+)." -Johannsen, 1908

Gypsum Plate

"Determination of the optical character of a uniaxial crystal with the gypsum plate when the center…

"Determination of the optical character of a biaxial crystal in a section cut perpendicular to the acute bisectrix by means of the gypsum plate (+)." -Johannsen, 1908

Gypsum Plate

"Determination of the optical character of a biaxial crystal in a section cut perpendicular to the acute…

"Determination of the optical character of biaxial crystals in sections showing the emergence of an optic axis by means of the gypsum plate." -Johannsen, 1908

Gypsum Plate

"Determination of the optical character of biaxial crystals in sections showing the emergence of an…

"Terminated usually by a combination of a positive and negative rhombohedron, which often are so equally developed as to give the effect of a hexagonal pyramid." — Ford, 1912

Quartz

"Terminated usually by a combination of a positive and negative rhombohedron, which often are so equally…

"Terminated usually by a combination of a positive and negative rhombohedron, which often are so equally developed as to give the effect of a hexagonal pyramid. Sometimes one rhombohedron predominates or occurs alone. At times the prism faces are wanting, and the combination of the two rhombodendrons gives what appears to be a doubly terminated hexagonal pyramid, known as a quartzoid." — Ford, 1912

Quartz

"Terminated usually by a combination of a positive and negative rhombohedron, which often are so equally…

This illustration shows Quartz or Silica. Quarts is the most abundant mineral in the Earth's continental crust.

Quartz

This illustration shows Quartz or Silica. Quarts is the most abundant mineral in the Earth's continental…

Well-rounded quartz grains from ancient eolian rock, enlarged by secondary addition of silica in optical continuity with the old quartz.

Quartz Grains

Well-rounded quartz grains from ancient eolian rock, enlarged by secondary addition of silica in optical…

Thin section of quartz sandstone shown under the microscope. The original rounded quartz grains are surrounded by new quartz, forming quartzite.

Quartz Sandstone

Thin section of quartz sandstone shown under the microscope. The original rounded quartz grains are…

"The quartz crystals are said to be right or left handed, depending upon whether these faces are to be observed trunctuating the edges between prism and rhombohedron." — Ford, 1912

Left-handed quartz

"The quartz crystals are said to be right or left handed, depending upon whether these faces are to…

"The quartz crystals are said to be right or left handed, depending upon whether these faces are to be observed trunctuating the edges between prism and rhombohedron." — Ford, 1912

Right-handed quartz

"The quartz crystals are said to be right or left handed, depending upon whether these faces are to…