Transmitted Light
Very common monoclinic amphibole, typical of metamorphic rocks.
PPL: Pale green colors, may be yellowish. Long prisms, fibers. Basal rhombic sections with 2 cleavages at 56-124º.
XPL: 1st and 2nd order colors (diagnostic against green hornblende!). Extinction 10-15º, ES(+), frequent twins and zoning. B(-) with 2V of 80º.
Images: Actinolite in PPL and in XPL.
Extremely common monoclinic phyllosilicate, occurs in many types of rocks.
PPL: Pale green colors with weak pleochroism. Very small lamellae, fibers or masses.
XPL: Anomalous colors: blue (berlin blue) or brown (leather brown), bluish-gray or purple. 0-9º extinction, unmottled (diagnostic against micas!). ES(+/-), B(+/-).
Images: Chloritized phenocryst in volcanic rock, in PPL and in XPL.
Common clay mineral in volcanic rocks.
PPL: Pleochroic from light green to yellow-green or blue-green. Moderate relief, forms submicroscopic crystal aggregates.
XPL: Color is almost the same. Simulate parallel extinction. B(-).
Images: Vesicle filled with celadonite in basalt, in PPL and in XPL.
Common phyllosilicate, exclusive of marine sediments and sedimentary rocks.
PPL: Pleochroic between green, yellow, olive and blue-green.
XPL: Continues with the green colors. Almost parallel extinction. B(-).
Images: Glauconite in sedimentary rock, in PPL and in XPL.
Common monoclinic sorosilicate, occurrs in many types of rocks.
PPL: Pleochroic between colorless, lime green, pale green, pale yellow, yellow-green and brown-green. High relief. Granular, columnar, acicular. Basal sections are rhombic. 1 perfect cleavage.
XPL: Intense and zoned anomalous colors. Paralell or oblique extinction. ES(+/-), B(-), 2V = 64-90º.
Images: Epidote in PPL and in XPL.
Rather rare monoclinic sorosilicate, typical of specific metamorphic rocks.
PPL: Weak to moderate pleochroism between colorless, yellowish, light green and blue-green. Lamellar, acicular or fibrous. Medium to high relief, 2 good cleavages.
XPL: Colors between 1st and 2nd order or anomalous (indigo blue and leather brown). Zoning common. ES(+/-), twins common, B(+), 2V 7º-110º.
Image not available yet.
Rather common orthorhombic nesosilicate, of Al-rich metamorphic rocks.
PPL: Usually colorless, may have pale green to pink pleochroism. Short prisms of square section. Perfect {110} cleavage; basal sections with 2 cleavages at 89º.
XPL: Paralell extinction, basal sections with symmetrical extinction. ES(-). Black carbon inclusions common. B(-), 2V:71-86°.
Images: Andalusite basal sections in PPL and in XPL.
Very common monoclinic pyroxene.
PPL: Usually colorless, but may have pale green, brown, yellow, or bluish pleochroism. Medium-high relief. Two cleavages at ~90º in the basal sections.
XPL: Oblique extinction (35-48º). ES(+). Twins common. B(+), 2V from 25-61°. Identical to diopside and pigeonite!
Images: Augite in PPL and in XPL.
Common monoclinic pyroxene, less common than augite.
PPL: Usually colorless, but can be pale green in color with very weak pleochroism. Medium to high relief. 2 cleavages at ~90º in basal sections. Granular to short prismatic.
XPL: Colors up to 2nd order orange. Extinction 38-48º, B(+), 2V 58-62º. Identical to augite and pigeonite!
Images: Diopside in PPL and XPL.
Rare monoclinic Ca-poor pyroxene, typical of volcanic rocks..
PPL: Usually colorless, can be pale, yellow-green to brownish-green in color. Medium-high relief, typically granular and anhedral, usually in the rock matrix.
XPL: Intense 2nd order colors. Oblique extinction from 37-44º, B(+) with 2V from 0-30º. Identical do augite and diopside!
Images: Pigeonite in PPL and in XPL.
Rare monoclinic pyroxene restricted to metamorphic rocks of the eclogite facies.
PPL: Usually colorless, may be pleochroic to very pale green. High relief.
XPL: Colors up to 3rd order. Oblique extinction, common twins, B(+). Identical to augite and diopside.
Images: Omphacite in PPL and in XPL.
Very rare monoclinic amphibole of Ca-poor metamorphic rocks.
PPL: Usually colorless, but can be pleochroic between pale green to pale brown. Forms clusters of prismatic crystals. In the basal section (rhombic!), 2 cleavages at 56/124º.
XPL: Extinction 15-21º. Colors up to 2nd and 3rd order. ES(+), B(+/-).
Image not yet available.
Rather common orthorhombic sulphate, of many different geological settings.
PPL: Usually colorless, but may be weakly pleochroic in green, yellow, violet, brown, or blue. Granular or tabular habit, forms radiated aggregates. Medium relief and several cleavages.
XPL: Lower 1st order colors, like gray to straw yellow, ES(+) and parallel extinction. Twins rare, zonation absent. B(+).
Images: Barite in XPL.
Rather common monoclinic sorosilicate, of the Allanite Group.
PPL: Usually pleochroic in red-brown, but can be in green colors. Zoning common. High relief, no visible cleavage. Anhedral or tabular grains.
XPL: Colors up to 3rd order. Pleochroic (black) halos are possible, may be metamictic. Twins common. B(-/+). Similar to brown hornblende.
Images: Allanite in PPL and in XPL.
Orthorhombic pyroxene common in ultramafic and basaltic rocks.
PPL: Usually pleochroic between pinkish and colorless, but may be pale green. Short prismatic, granular, basal section with 4 or 8 sides and 2 cleavages at ~90º.
XPL: Parallel extinction! Colors up to 1st order orange (lower than the colors of clinopiroxenes!). ES(+), common zonation, rare twins. B(+/-), 2V from 58-86°.
Images: Enstatite in PPL and in XPL.
Common monoclinic acessory phosphate.
PPL: Usually colorless or yellow, but may show weak pale green pleochroism. High relief, without visible cleavage, in rounded or wedge-shaped grains. Black halos around it are possible.
XPL, intense 2nd and 3rd order colors. Parallel extinction, B(+), 2V = 6-19º. Very similar to zircon. Can be confused with epidote.
Images: Monazite in PPL and in XPL.
