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"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…