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!

UNC sample

CA-75

Rock type

?

Locality

?