Amphibole Glaucophane Note the purple to blue-gray pleochroism in the glaucophane in this slide. UNC sample ? Rock type blueschist Locality unknown Glaucophane Note the anomalous blue-gray interference colors in the glaucophane in this slide. UNC sample ? Rock type blueschist Locality unknown
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Amphibole
Glaucophane
Note the purple to blue-gray pleochroism in the glaucophane in this slide.
UNC sample
?
Rock type
blueschist
Locality
unknown
Glaucophane
Note the anomalous blue-gray interference colors in the glaucophane in this slide.
UNC sample
?
Rock type
blueschist
Locality
unknown
Amphibole
Hornblende
Note the characteristic ~120 degree cleavage angles in some sections and the brown to green. pleochroism.
UNC sample
W-86
Rock type
hornblende-cpx schist
Locality
unknown
Hornblende
Note in some sections the ~120 degree cleavage angles which are diagnostic of amphiboles.
UNC sample
W-86
Rock type
hornblende-cpx schist
Locality
unknown
Amphibole
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.
UNC sample
W-88
Rock type
talc-tremolite schist
Locality
unknown
Andalusite
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.
UNC sample
NM-1
Rock type
andalusite-biotite schist
Locality
New Mexico
Mica
Biotite
Note the red-brown pleochroism and the characteristic black pleochroic haloes (caused by radiation damage).
UNC sample
GSR X0720
Rock type
garnet-mica schist
Locality
unknown
Biotite
Note the anomalous red interference color.
UNC sample
GSR X0720
Rock type
garnet-mica schist
Locality
unknown
Mica
Muscovite
UNC sample
GSR 1540
Rock type
unknown
Locality
unknown
Muscovite
This grain is shown at maximum birefringnence.
Take a look at this grain at extinction to see muscovite's wonderful "bird's eye" mottling.
UNC sample
GSR 1540
Rock type
unknown
Locality
unknown
Sericite (a fine-grained variety of muscovite)
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.
UNC sample
BB-13
Rock type
Alaskite
Locality
Montana
Calcite
Note the rhombohedral cleavage.
UNC sample
GSR X5321
Rock type
unknown
Locality
unknown
Calcite
Note the rhombohedral cleavage and very high order interference colors.
UNC sample
GSR X5321
Rock type
unknown
Locality
unknown
Chlorite
Chlorite defines the foliation in this rock, which also shows some crenulation cleavage.
UNC sample
MIC-5c
Rock type
chlorite schist
Locality
Michigan
Chloritoid
This plane-light view highlights the sector zoning in these chloritoid porphyroblasts.
UNC sample
EU-310
Rock type
chloritoid schist
Locality
?
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.
UNC sample
EU-310
Rock type
chloritoid schist
Locality
?
Ellenbergerite
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.
UNC sample
TS-40
(K. Stewart)
Rock type
qtz-ky-gt-musc schist
Locality
Dora Maira massif, Parigi, Italy
Epidote
Note the fairly high relief of epidote, the highly fractured mineral in this photomicrograph.
UNC sample
EU-81
Rock type
Biotite granite gneiss
Locality
Moine, Scotland
Epidote
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.
UNC sample
EU-81
Rock type
Biotite granite gneiss
Locality
Moine, Scotland
Microcline (K-feldspar)
Cross-hatched (or "tartan") twinning in microcline. Contrast this with polysynthetic twinning in plagioclase feldspar.
UNC sample
GSR X1540
Rock type
unknown
Locality
unknown
Feldspar
Plagioclase
This slide showcases one of plagioclase's very common features: its polysynthetic twinning. Contrast this with twinning in microcline (K-feldspar).
UNC sample
WR-51
Rock type
unknown
Locality
unknown
Garnet
Note the zonal distribution of quartz inclusions in this garnet porphyroblast.
UNC sample
GSR X0720
Rock type
garnet-mica schist
Locality
unknown
Garnet
Note the zonal distribution of quartz inclusions in this garnet porphyroblast.
UNC sample
GSR X0720
Rock type
garnet-mica schist
Locality
unknown
Kyanite
Note the prismatic habit of kyanite.
UNC sample
NC-349
Rock type
kyanite-garnet-
mica schist
Locality
near Durham, NC
Kyanite
Note the first-order interference colors and prismatic habit of kyanite.
UNC sample
NC-349
Rock type
kyanite-garnet-
mica schist
Locality
near Durham, NC
Leucite
UNC sample
1790 (card)
Rock type
leucite basalt
Locality
unknown
Leucite
Note the nearly isotropic nature of these leucite grains.
UNC sample
1790 (card)
Rock type
leucite basalt
Locality
unknown
Nepheline
Many of the phenocrysts in this basalt are nepheline.
UNC sample
H-99
Rock type
nepheline basalt
Locality
unknown
Olivine
Almost all of the grains in this rock are olivine. Note the high order interference colors and the minor secondary calcite.
UNC sample
W-44
Rock type
dunite
Locality
unknown
Augite (Clinopyroxene)
Note the pigeonite twin lamellae in this grain. Pigeonite is a Ca-poor clinopyroxene.
UNC sample
in "norite" card
Rock type
clinopyroxenite
Locality
West Point, GA
Augite (Clinopyroxene)
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.
UNC sample
"norite" card
Rock type
clinopyroxenite
Locality
West Point, GA
Hypersthene (Orthopyroxene)
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.
UNC sample
PP-12
Rock type
bronzitite (orthopyroxenite)
Locality
Stillwater complex, MT
Hypersthene (Orthopyroxene)
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.
UNC sample
PP-12
Rock type
bronzitite (orthopyroxenite)
Locality
Stillwater complex, MT
Piemontite
Piemontite has beautiful rose to yellow pleochroism.
UNC sample
?
Rock type
unknown
Locality
unknown
Piemontite
Piemontite has beautiful, high-order interference colors.
UNC sample
?
Rock type
unknown
Locality
unknown
Quartz
UNC sample
GSR X1540
Rock type
unknown
Locality
unknown
Quartz
This slide shows quartz in a range of crystal orientations, all having low-first order interference colors.
UNC sample
GSR X1540
Rock type
unknown
Locality
unknown
Coesite
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).
UNC sample
TS-41
(K. Stewart)
Rock type
qtz-ky-gt-musc schist
Locality
Dora Maira massif, Parigi, Italy
Quartz after coesite
The region of coarser-grained quartz in the upper center portion of this photomicrograph was probably originally occopied by coesite, the high-pressure polymorph of quartz. Metamorphic rocks from the Dora Maira Massif show other evidence of being exhumed from EXTREMELY deep levels in thickened crust.
UNC sample
TS-42
(K. Stewart)
Rock type
qtz-ky-gt-musc schist
Locality
Dora Maira Massif, Parigi, Italy
Staurolite
The "swiss cheese" look (i.e., poikiloblastic texture) of these staurolite porphyroblasts is typical for this mineral. Also note the strong banana yellow pleochroism.
UNC sample
EU-17
Rock type
staurolite-kyanite -garnet-mica schist
Locality
?
Staurolite
The "swiss cheese" look (i.e., poikiloblastic texture) of these staurolite porphyroblasts is typical for this mineral.
UNC sample
EU-17
Rock type
staurolite-kyanite -garnet-mica schist
Locality
?
Stilpnomelane
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.
UNC sample
L-11
Rock type
garnet-stilp- muscovite schist
Locality
?
Stilpnomelane
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.
UNC sample
L-11
Rock type
garnet-stilp- muscovite schist
Locality
?
Talc
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.
UNC sample
W-88
Rock type
talc-tremolite schist
Locality
unknown
Titanite (Sphene)
Titanite typically forms wedge-shaped crystals like this one. Also notice the extremely high relief.
UNC sample
EU-290
Rock type
syenite
Locality
?
Titanite (Sphene)
Titanite typically forms wedge-shaped crystals like this one. Also notice the extremely high interference colors.
UNC sample
EU-290
Rock type
syenite
Locality
?
Tourmaline
This slide shows zoned trigonal cross-sections and elongate sections. Note green to brown pleochroism. Tourmaline may also display bluish pleochroism.
UNC sample
?
Rock type
unknown
Locality
unknown
Tourmaline
This slide shows extinct trigonal cross-sections and elongate sections displaying maximum birefringence. The matrix is quartz.
UNC sample
?
Rock type
unknown
Locality
unknown
Vesuvianite (Idocrase)
A fairly uninteresting photo here.
UNC sample
CA-75
Rock type
?
Locality
?
Vesuvianite (Idocrase)
Vesuvianite displays the deepest indigo blue anomalous interference colors you've ever seen!