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Gypsum.

Gypsum

Gypsum.

Gypsum.

Gypsum

Gypsum.

"Monoclinic. Crystals usually tabular parallel to clinopinacoid; in diamond-shaped crystals with edges beveled by prism and pyramid faces." — Ford, 1912

Gypsum

"Monoclinic. Crystals usually tabular parallel to clinopinacoid; in diamond-shaped crystals with edges…

"Monoclinic. Crystals usually tabular parallel to clinopinacoid; in diamond-shaped crystals with edges beveled by prism and pyramid faces. Other forms rare. Sometimes twinned." — Ford, 1912

Gypsum

"Monoclinic. Crystals usually tabular parallel to clinopinacoid; in diamond-shaped crystals with edges…

"Vertical section through a Gulf Coast salt dome." -Johnson, 1916

Salt Dome

"Vertical section through a Gulf Coast salt dome." -Johnson, 1916

"...to be cut in half by this plane (the twinned plane, reference Twinned Crystal of Gypsum) and one portion to be rotated through 180 degrees about the normal to the same plane. Described as being twinned on the plane." -The Encyclopedia Britannica 1910

Simple Crystal of Gypsum

"...to be cut in half by this plane (the twinned plane, reference Twinned Crystal of Gypsum) and one…

"...the two portions are symmetrical with respect to a plane parallel to the ortho-pinacoid." -The Encyclopedia Britannica 1910

Twinned Crystal of Gypsum

"...the two portions are symmetrical with respect to a plane parallel to the ortho-pinacoid." -The Encyclopedia…