Amphibole Glaucophane blue Note the purple to blue-gray pleochroism in the glaucophane in this slide. Glaucophane blue Note the anomalous blue-gray interference colors in the glaucophane in this slide.
Amphibole Hornblende W-86 hornblende-cpx Note the characteristic ~120 degree cleavage angles in some sections and the brown to green. pleochroism. Hornblende W-86 hornblendecpx Note in some sections the ~120 degree cleavage angles which are diagnostic of amphiboles.
Tremolite Amphibole W-88 talc-tremolite Talc forms the fine-grained matrix between the prismatic crystals of tremolite in this rock. Note the ~120 degree cleavages in some of the tremolite sections.
Andalusite NM-1 andalusite-biotite New Mexico This is an andalusite porphyroblast with poikiloblastic texture. Also note how the foliation (oriented roughly N-S in this view) is wrapped around the left and right corners of this grain, suggesting synkinematic growth of the andalusite porphyroblast.
Mica Biotite GSR X0720 garnet-mica Note the red-brown pleochroism and the characteristic black pleochroic haloes (caused by radiation damage). Biotite GSR X0720 garnet-mica Note the anomalous red interference color.
Mica Muscovite GSR 1540 Muscovite GSR 1540 This grain is shown at maximum birefringnence. Take a look at this grain at extinction to see muscovite's wonderful "bird's eye" mottling.
Sericite (a fine-grained variety of muscovite) BB-13 Alaskite Montana The feldspars in this alaskite from the Boulder Batholith have been largely replaced by fine-grained muscovite (sericite). In this rock, sericite is a product of hydrothermal alteration.
Calcite GSR X5321 Note the rhombohedral cleavage. Calcite GSR X5321 Note the rhombohedral cleavage and very high order interference colors.
Chlorite MIC-5c chlorite Michigan Chlorite defines the foliation in this rock, which also shows some crenulation cleavage.
Chloritoid EU-310 chloritoid This plane-light view highlights the sector zoning in these chloritoid porphyroblasts. Chloritoid EU-310 chloritoid These stubby crystals are chloritoid porphyroblasts. You can just barely see the anomalous green interference color at the edge of some of the grains. Despite the name, chloritoid really doesn't look anything like chlorite.
Ellenbergerite TS-40 (K. Stewart) qtz-ky-gtmusc Dora Maira massif, Parigi, Italy The dark reddish-purple grain in the center of this photomicrograph is ellenbergerite, an extremely rare, high-pressure Mg-Al-Ti-silicate, which here forms an inclusion in nearly pure endmember pyrope garnet from the famous Dora Maira massif of Italy.
Epidote EU-81 Biotite granite gneiss Moine, Scotland Note the fairly high relief of epidote, the highly fractured mineral in this photomicrograph. Epidote EU-81 Biotite granite gneiss Moine, Scotland Note the high-order interference colors of epidote. This slide is actually cut a little thin, and doesn't show the third-order colors that epidote may display in some sections.
Microcline (K-feldspar) GSR X1540 Cross-hatched (or "tartan") twinning in microcline. Contrast this with polysynthetic twinning in plagioclase feldspar.
Plagioclase Feldspar WR-51 This slide showcases one of plagioclase's very common features: its polysynthetic twinning. Contrast this with twinning in microcline (Kfeldspar).
Garnet GSR X0720 garnet-mica Note the zonal distribution of quartz inclusions in this garnet porphyroblast. Garnet GSR X0720 garnet-mica Note the zonal distribution of quartz inclusions in this garnet porphyroblast.
Kyanite NC-349 kyanite-garnet- mica near Durham, NC Note the prismatic habit of kyanite. Kyanite NC-349 kyanite-garnet- mica near Durham, NC Note the first-order interference colors and prismatic habit of kyanite.
Leucite 1790 (card) leucite basalt Leucite 1790 (card) leucite basalt Note the nearly isotropic nature of these leucite grains.
Nepheline H-99 nepheline basalt Many of the phenocrysts in this basalt are nepheline.
Olivine W-44 dunite Almost all of the grains in this rock are olivine. Note the high order interference colors and the minor secondary calcite.
Augite (Clinopyroxene) in "norite" card clinopyroxenite West Point, GA Note the pigeonite twin lamellae in this grain. Pigeonite is a Ca-poor clinopyroxene. Augite (Clinopyroxene) "norite" card clinopyroxenite West Point, GA Note the pigeonite twin lamellae in this grain. Pigeonite is a Ca-poor clinopyroxene. Besides clinopyroxene's 2nd order colors, another way to distinguish clinopyroxene from orthopyroxene is by clinopyroxene's inclined extinction.
Hypersthene (Orthopyroxene) PP-12 bronzitite (orthopyroxenite) Stillwater complex, MT Hypersthene can be identified from its characteristic rose-colored pleochroism which is exhibited by the grain in the center. Watch what happens to the color of this grain upon rotation of the stage. Hypersthene (Orthopyroxene) PP-12 bronzitite (orthopyroxenite) Stillwater complex, MT Orthopyroxenes are noted for having low, first-order interference colors. Also note the cleavages that intersect at about 90 degrees. Another identifying characteristic of orthopyroxene is its parallel extinction.
Piemontite Piemontite has beautiful rose to yellow pleochroism. Piemontite Piemontite has beautiful, high-order interference colors.
Quartz GSR X1540 Quartz GSR X1540 This slide shows quartz in a range of crystal orientations, all having lowfirst order interference colors.
Coesite TS-41 (K. Stewart) qtz-ky-gt-musc Dora Maira massif, Parigi, Italy Coesite (center of inclusion) and recrystallized quartz (borders of inclusion) form a tiny inclusion in nearly pure endmember pyrope garnet from the famous Dora Maira massif of Italy. The presence of coesite (a high-pressure polymorph of quartz) indicates that this rock saw extremly high pressures during metamorphism (probably more than 28 kbar).
Quartz after coesite TS-42 (K. Stewart) qtz-ky-gt-musc Dora Maira Massif, Parigi, Italy The region of coarser-grained quartz in the upper center portion of this photomicrograph was probably originally occopied by coesite, the highpressure polymorph of quartz. Metamorphic rocks from the Dora Maira Massif show other evidence of being exhumed from EXTREMELY deep levels in thickened crust.
Staurolite EU-17 staurolitekyanite - garnet-mica The "swiss cheese" look (i.e., poikiloblastic texture) of these staurolite porphyroblasts is typical for this mineral. Also note the strong banana yellow pleochroism. Staurolite EU-17 staurolitekyanite - garnet-mica The "swiss cheese" look (i.e., poikiloblastic texture) of these staurolite porphyroblasts is typical for this mineral.
Stilpnomelane L-11 garnet-stilpmuscovite Stilpnomelane looks alot like biotite (same habit and color) but lacks the "bird's eye" extinction that biotite displays. Actually, the stilpnomelane in this slide has a more acicular habit than most biotite. Stilpnomelane L-11 garnet-stilpmuscovite Stilpnomelane looks alot like biotite (same habit and color) but lacks the "bird's eye" extinction that biotite displays. Actually, the stilpnomelane in this slide has a more acicular habit than most biotite.
Talc W-88 talc-tremolite Talc forms the fine-grained matrix between the prismatic crystals of tremolite in this rock. Note the fine-grain size and the extremely high interference colors of the talc.
Titanite (Sphene) EU-290 syenite Titanite typically forms wedge-shaped crystals like this one. Also notice the extremely high relief. Titanite (Sphene) EU-290 syenite Titanite typically forms wedge-shaped crystals like this one. Also notice the extremely high interference colors.
Tourmaline This slide shows zoned trigonal cross-sections and elongate sections. Note green to brown pleochroism. Tourmaline may also display bluish pleochroism. Tourmaline This slide shows extinct trigonal cross-sections and elongate sections displaying maximum birefringence. The matrix is quartz.
Vesuvianite (Idocrase) CA-75 A fairly uninteresting photo here. Vesuvianite (Idocrase) CA-75 Vesuvianite displays the deepest indigo blue anomalous interference colors you've ever seen!