ClipArt ETC
"A positive biaxial interference figure with the principal sections nearly corresponding to those of the nicols. The arrows indicate the movement taking place upon inserting a quartz wedge above the section." -Johannsen, 1908

Biaxial Interference

"A positive biaxial interference figure with the principal sections nearly corresponding to those of…

"A biaxial interference figure showing the emergence of an optic axis. The arrow indicates the movement taking place upon inserting a quartz wedge above the section. The mineral is augite. (+)." -Johannsen, 1908

Biaxial Interference

"A biaxial interference figure showing the emergence of an optic axis. The arrow indicates the movement…

"A negative biaxial interference figure. The arrows indicate the movement taking place upon inserting a quartz wedge above the section. Epidote. (-)." -Johannsen, 1908

Negative Biaxial Interference

"A negative biaxial interference figure. The arrows indicate the movement taking place upon inserting…

"A positive biaxial interference figure. The arrows indicate the movement taking place upon inserting a quartz wedge above the section. Olivine. (+)." -Johannsen, 1908

Positive Biaxial Interference

"A positive biaxial interference figure. The arrows indicate the movement taking place upon inserting…

"Movement of the left bar...upon rotating the stage to the right, and movement of the colored rings upon inserting a quartz wedge." -Johannsen, 1908

Crystal Movement

"Movement of the left bar...upon rotating the stage to the right, and movement of the colored rings…

"Crossed dispersion in a monoclinic crystal p>v." -Johannsen, 1908

Crossed Dispersion

"Crossed dispersion in a monoclinic crystal p>v." -Johannsen, 1908

"Horizontal dispersion in a monoclinic crystal. p<v." -Johannsen, 1908

Horizontal Dispersion

"Horizontal dispersion in a monoclinic crystal. p

"Inclined dispersion in a monoclinic crystal. Diopside, p>v." -Johannsen, 1908

Inclined Dispersion

"Inclined dispersion in a monoclinic crystal. Diopside, p>v." -Johannsen, 1908

"Maximum extinction angles in the Pyroxene and Amphibole groups. Solid lines indicate extinction angles from c to c; broken lines from c to a. The extinction angle in an amphibole is generally less than 23 degrees; in a pyroxene it is generally greater. " -Johannsen, 1908

Extinction Angles

"Maximum extinction angles in the Pyroxene and Amphibole groups. Solid lines indicate extinction angles…

"Positive and negative extinction angles in the feldspars." -Johannsen, 1908

Extinction Angles

"Positive and negative extinction angles in the feldspars." -Johannsen, 1908

"Extinction angles on the (001) faces of the lime-soda feldspars." -Johannsen, 1908

Extinction Angles

"Extinction angles on the (001) faces of the lime-soda feldspars." -Johannsen, 1908

"Extinction angles on the (010) faces of the lime-soda feldspars." -Johannsen, 1908

Extinction Angles

"Extinction angles on the (010) faces of the lime-soda feldspars." -Johannsen, 1908

"The (010) plane of an orthoclase crystal." -Johannsen, 1908

Orthoclase Crystal

"The (010) plane of an orthoclase crystal." -Johannsen, 1908

"The (001) plane of an orthoclase crystal." -Johannsen, 1908

Orthoclase Crystal

"The (001) plane of an orthoclase crystal." -Johannsen, 1908

A simple orthoclase crystal.

Orthoclase Crystal

A simple orthoclase crystal.

A simple orthoclase crystal.

Orthoclase Crystal

A simple orthoclase crystal.

A simple orthoclase crystal.

Orthoclase Crystal

A simple orthoclase crystal.

"Simple orthoclase crystal showing cleavage lines and the position of the twinning plane in a Carlsbad twin." -Johannsen, 1908

Orthoclase Crystal

"Simple orthoclase crystal showing cleavage lines and the position of the twinning plane in a Carlsbad…

"Simple orthoclase crystal opened out to show the optical orientation." -Johannsen, 1908

Orthoclase Crystal

"Simple orthoclase crystal opened out to show the optical orientation." -Johannsen, 1908

"A Carlsbad twin of orthoclase." -Johannsen, 1908

Orthoclase Twin

"A Carlsbad twin of orthoclase." -Johannsen, 1908

"A Baveno twin of orthoclase." -Johannsen, 1908

Orthoclase Twin

"A Baveno twin of orthoclase." -Johannsen, 1908

"Section through an orthorhombic crystal with p>v." -Johannsen, 1908

Orthorhombic Crystal

"Section through an orthorhombic crystal with p>v." -Johannsen, 1908

"A (010) cleavage flake of plagioclase." -Johannsen, 1908

Plagioclase

"A (010) cleavage flake of plagioclase." -Johannsen, 1908

"Cross-sections at right angles to both (001) and (010) showing (+) and (-) character of extinction in plagioclase feldspars." -Johannsen, 1908

Plagioclase Feldspars

"Cross-sections at right angles to both (001) and (010) showing (+) and (-) character of extinction…

"The (010) face of a Carlsbad twin of plagioclase." -Johannsen, 1908

Plagioclase Twin

"The (010) face of a Carlsbad twin of plagioclase." -Johannsen, 1908

"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…

"Determination of the optical character of a uniaxial crystal with the mica plate. (a) Positive. (b) Negative." -Johannsen, 1908

Mica Plate

"Determination of the optical character of a uniaxial crystal with the mica plate. (a) Positive. (b)…

"Albite and Carlsbad twinning combined." -Johannsen, 1908

Twinning

"Albite and Carlsbad twinning combined." -Johannsen, 1908

"A positive uniaxial interference figure. The arrows indicate the movement taking place upon inserting a quartz wedge above the section." -Johannsen, 1908

Uniaxial Interference

"A positive uniaxial interference figure. The arrows indicate the movement taking place upon inserting…