Minerals in Thin Section _1

Amphibole

Glaucophane

UNC sample ? Rock type blueschist Locality unknown

Note the purple to blue-gray pleochroism in the glaucophane in this slide.

Glaucophane

UNC sample ? Rock type blueschist Locality unknown

Note the anomalous blue-gray interference colors in the glaucophane in this slide.

Amphibole

Hornblende

UNC sample W-86 Rock type hornblende-cpx schist Locality unknown

Note the characteristic ~120 degree cleavage angles in some sections and the brown to green. pleochroism.

Hornblende

UNC sample W-86 Rock type hornblendecpx schist Locality unknown

Note in some sections the ~120 degree cleavage angles which are diagnostic of amphiboles.

Amphibole

Tremolite

UNC sample W-88 Rock type talc-tremolite schist Locality unknown

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

UNC sample NM-1 Rock type andalusite-biotite schist Locality 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

UNC sample GSR X0720 Rock type garnet-mica schist Locality unknown

Note the red-brown pleochroism and the characteristic black pleochroic haloes (caused by radiation damage).

Biotite

UNC sample GSR X0720 Rock type garnet-mica schist Locality unknown

Note the anomalous red interference color.

Mica

Muscovite

UNC sample GSR 1540 Rock type unknown Locality unknown

Muscovite

UNC sample GSR 1540 Rock type unknown Locality unknown

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)

UNC sample BB-13 Rock type Alaskite Locality 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

UNC sample GSR X5321 Rock type unknown Locality unknown

Note the rhombohedral cleavage.

Calcite

UNC sample GSR X5321 Rock type unknown Locality unknown

Note the rhombohedral cleavage and very high order interference colors.

Chlorite

UNC sample MIC-5c Rock type chlorite schist Locality Michigan

Chlorite defines the foliation in this rock, which also shows some crenulation cleavage.

Chloritoid

UNC sample EU-310 Rock type chloritoid schist Locality ?

This plane-light view highlights the sector zoning in these chloritoid porphyroblasts.

Chloritoid

UNC sample EU-310 Rock type chloritoid schist Locality ?

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

UNC sample TS-40 (K. Stewart) Rock type qtz-ky-gtmusc schist Locality 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

UNC sample EU-81 Rock type Biotite granite gneiss Locality Moine, Scotland

Note the fairly high relief of epidote, the highly fractured mineral in this photomicrograph.

Epidote

UNC sample EU-81 Rock type Biotite granite gneiss Locality 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)

UNC sample GSR X1540 Rock type unknown Locality unknown

Cross-hatched (or "tartan") twinning in microcline. Contrast this with polysynthetic twinning in plagioclase feldspar.

Feldspar

Plagioclase

UNC sample WR-51 Rock type unknown Locality unknown

This slide showcases one of plagioclase's very common features: its polysynthetic twinning. Contrast this with twinning in microcline (Kfeldspar).

Garnet

UNC sample GSR X0720 Rock type garnet-mica schist Locality unknown

Note the zonal distribution of quartz inclusions in this garnet porphyroblast.

Garnet

UNC sample GSR X0720 Rock type garnet-mica schist Locality unknown

Note the zonal distribution of quartz inclusions in this garnet porphyroblast.

Kyanite

UNC sample NC-349 Rock type kyanite-garnetmica schist Locality near Durham, NC

Note the prismatic habit of kyanite.

Kyanite

UNC sample NC-349 Rock type kyanite-garnetmica schist Locality near Durham, NC

Note the first-order interference colors and prismatic habit of kyanite.

Leucite

UNC sample 1790 (card) Rock type leucite basalt Locality unknown

Leucite

UNC sample 1790 (card) Rock type leucite basalt Locality unknown

Note the nearly isotropic nature of these leucite grains.

Nepheline

UNC sample H-99 Rock type nepheline basalt Locality unknown

Many of the phenocrysts in this basalt are nepheline.

Olivine

UNC sample W-44 Rock type dunite Locality unknown

Almost all of the grains in this rock are olivine. Note the high order interference colors and the minor secondary calcite.

Augite (Clinopyroxene)

UNC sample in "norite" card Rock type clinopyroxenite Locality West Point, GA

Note the pigeonite twin lamellae in this grain. Pigeonite is a Ca-poor clinopyroxene.

Augite (Clinopyroxene)

UNC sample "norite" card Rock type clinopyroxenite Locality 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)

UNC sample PP-12 Rock type bronzitite (orthopyroxenite) Locality 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)

UNC sample PP-12 Rock type bronzitite (orthopyroxenite) Locality 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

UNC sample ? Rock type unknown Locality unknown

Piemontite has beautiful rose to yellow pleochroism.

Piemontite

UNC sample ? Rock type unknown Locality unknown

Piemontite has beautiful, high-order interference colors.

Quartz

UNC sample GSR X1540 Rock type unknown Locality unknown

Quartz

UNC sample GSR X1540 Rock type unknown Locality unknown

This slide shows quartz in a range of crystal orientations, all having lowfirst order interference colors.

Coesite

UNC sample TS-41 (K. Stewart) Rock type qtz-ky-gt-musc schist Locality 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

UNC sample TS-42 (K. Stewart) Rock type qtz-ky-gt-musc schist Locality 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

UNC sample EU-17 Rock type staurolitekyanite garnet-mica schist Locality ?

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

UNC sample EU-17 Rock type staurolitekyanite garnet-mica schist Locality ?

The "swiss cheese" look (i.e., poikiloblastic texture) of these staurolite porphyroblasts is typical for this mineral.

Stilpnomelane

UNC sample L-11 Rock type garnet-stilpmuscovite schist Locality ?

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

UNC sample L-11 Rock type garnet-stilpmuscovite schist Locality ?

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

UNC sample W-88 Rock type talc-tremolite schist Locality unknown

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)

UNC sample EU-290 Rock type syenite Locality ?

Titanite typically forms wedge-shaped crystals like this one. Also notice the extremely high relief.

Titanite (Sphene)

UNC sample EU-290 Rock type syenite Locality ?

Titanite typically forms wedge-shaped crystals like this one. Also notice the extremely high interference colors.

Tourmaline

UNC sample ? Rock type unknown Locality unknown

This slide shows zoned trigonal cross-sections and elongate sections. Note green to brown pleochroism. Tourmaline may also display bluish pleochroism.

Tourmaline

UNC sample ? Rock type unknown Locality unknown

This slide shows extinct trigonal cross-sections and elongate sections displaying maximum birefringence. The matrix is quartz.

Vesuvianite (Idocrase)

UNC sample CA-75 Rock type ? Locality ?

A fairly uninteresting photo here.

Vesuvianite (Idocrase)

UNC sample CA-75 Rock type ? Locality ?

Vesuvianite displays the deepest indigo blue anomalous interference colors you've ever seen!