Petrology, GEO-320 – Kurt Hollocher

Petrology is the study of rocks, their composition, mineralogy, and origin. The detailed characteristics of chemistry, minerals, and mineral textures can lead to a detailed understanding of rock genesis. This information can then be used to address larger scale geologic issues, such as the tectonic development of mountain ranges and the eruptive history of volcanoes.

Special documents	Syllabus
	Using petrographic microscopes: adjustments and features
	Internet resources
	Exam study guides	Igneous rocks Metamorphic rocks
Igneous rock labs	White Mountain magma series	WMMS data set WMMS discussions 1, 2, 3 Photo gallery
	New Hampshire magma series	NHMS and Wooley Creek data sets NHMS discussions 1, 2, 3 Photo gallery
	Skaergaard and Stillwater intrusions	Skaergaard topics 1, 2, 3 Stillwater topics 1, 2, 3 Skaergaard photo gallery 1, 2. Stillwater photo gallery 1.
	Iceland lavas	Iceland lavas data set Iceland geology and discussions 1, 2, 3 Photo gallery
Metamorphic rock labs	New England schists	New England geology 1, 2; metamorphism 1, 2 New England schist discussions 1, 2 Photo gallery
	New England mafic rocks	New England geology 1, 2; metamorphism 1, 2 New England mafic discussions 1, 2, 3 Photo gallery
	Norwegian eclogites	Fennoscandia geologic map, very simplified map Geologic discussions 1, 2, 3 Photo gallery
	Fault rocks	Fault rock discussions 1, 2 Photo gallery
Forms and graph paper	Rock report form Ternary graph paper, and a green one
Documents and spreadsheet utilities	Writing igneous rock hand sample descriptions Writing metamorphic rock hand sample descriptions Papers to replace field trips Why petrology is so much fun
	How to calculate norms from rock chemical analyses NORM4 norm spreadsheet for single samples NORM4 macro-enabled version for multiple samples (file type not allowed here, ask me for a copy)
	Estimating Fe³⁺ in amphiboles Estimating Fe³⁺ in biotite Making thin sections Staining feldspars in thin section
	Fill in missing values on REE diagrams! Make ternary (triangle) diagrams in spreadsheets! Whole rock geochemical discriminant diagrams!
Image libraries	Igneous minerals in thin section Igneous textures in thin section Metamorphic minerals in thin section Metamorphic reactions in thin section Metamorphic microstructures in thin section Moon rocks Hand sketches in petrology
SVG vector graphics files for figures I use in this course (native Inkscape)

Assorted field trip images

Late fault offsetting quartzite layer.
Small fault with calcite infilling, cutting calc-silicate block in marble, Paradox.
David pops out of the boulder cave.
Normal-size samples are sufficient for normal people.
Charnockite gneiss near Schroon Lake.
Exposures of the Roaring Brook intrusion breccia, Giant Mountain, Adirondacks.
Black Precipice for lunch.
View from the summit to the south, toward Bald Rock (left) and the halfway house site (right).
Large tourmaline crystals in a quartz vein. Largest crystal is ~5 cm long.
Nice graded quartzite bed. Top is to the upper left.
Cambrian Cheshire quartzite on Pine Cobble, Williamstown, Massachusetts.
More folded quartzite beds. Wind is gusting to 50 mph.
Halfway house site, with andalump schist and pegmatite.
Summit of Mt. Jo.
Large garnets in melt pockets in an amphibolite.
Large twinned plagioclase, summit of Mt. Jo, in an anorthosite block within the leuconorite.
Petrology, 2000. Sarah, Nick, Mike, Bill, Sarah, Jeremy on the summit.
A new friend.
Lunch on Black Precipice, looking south at the landscape.
Sarah and Sarah walking up to Bald Rock.
Off the main trail, looking toward the summit.
Marble-matrix breccia near Paradox.
Chicken track pattern of andalumps on a foliation surface.
Boulder cave entrance.
Group photo from Pine Cobble, Williamstown, Massachusetts. Stop 4 at 9:00 AM.
More lunch on Black Precipice.
Magnetite ore body and mine west of Ticonderoga, NY.
Boulder cave exit, again.
Largest plagioclase megacryst in anorthosite, Mt. Jo.
Looking down on Heart Lake, adjacent to the Adirondack Loj campground.
Coarse-grained, intensely folded graphite- and diopside-bearing marble on the shores of the Hudson River, Warrensburg, NY.
The true breakfast, lunch, and dinner of champions.
And snacks, too!
Looking at Clough Quartzite, Cragg Mountain trail, Northfield, MA.
Eroded lamprophyre dike, near the summit of Mt. Jo.
Ferrosyentie dike cutting leuconorite, summit of Mt. Jo.
Labradorite showing labradorescence. It is caused by a diffraction effect from closely-spaced exsolution lamellae.
End of the trip on the summit of Crag Mountain, on Silurian Clough quartzite which is made out of deformed quartz pebbles and cobbles.
Looking southwest from the top of Roaring Brook falls, Giant Mountain, Adirondacks.
Folded marble, West Stockbridge Formation, Natural Bridge Park, North Adams, Massachusetts. Photo donated by Ralf Schauer.
Summit of Monadnock.
Portrait of an unhappy snake.
Praying for divine guidance: what is that soft, flakey, metallic mineral in this marble?
Coarse-grained marble on the shores of the Hudson River.
Looking at metamorphosed quartz pebble conglomerate in the Cheshire Quartzite, Pine Cobble Trail, Williamstown, MA.
Summit of Monadnock.
Looking at metamorphosed quartz pebble conglomerate in the Cheshire Quartzite, Pine Cobble Trail, Williamstown, MA.
Boulder cave exit.
Eroded lamprophyre dike, near the summit of Mt. Jo.
Sarah, done with her sandwich. Not sure if it was the finest.
Looking at a thin ferrogabbro dike crosscutting anorthosite.
Trying to get out to the outcrop in the middle of the river, Jay.
Fold hinge in one of the isoclinally folded quartzite beds.
The whole hiking crew.
Part of the class.
Metamorphosed limestone of the West Stockbridge Formation, North Adams, Massachusetts.
Large sillimanite pseudomorph after andalusite, ~35 cm long.
Early risers in Petrology, 2004.
Rainwater pool off the main trail, looking southeast toward Bald Rock.
Contact between a granitic gneiss (light colored center and right) and a garnet amphibolite (lower left).
Outcrop of Clough Quartzite on Crag Mountain, Erving, Massachusetts. View to south-southeast toward the Northfield Mountain pumped storage reservoir in the Pelham Dome.
Searching for mega-samples, as usual.
Highly deformed marble on the shores of the Hudson River.
Group photo on Crag Mountain, Erving, Massachusetts, view to northeast.
Blue calcite!
Metamorphosed Cambro-Ordovician volcaniclastic sediments on the east side of the Berkshires. Abundant quartz veins and glacial striations.
Looking back toward the summit from Bald Rock, on the way to the graphite mine and the boulder cave.
Looking back from the location above to the Billings Fold itself.
Samples of magnetite-garnet sand, Schroon River.
Summit of Monadnock.
Paying homage to partially recrystallized (Whiteface Mtn. type) anorthosite.
The Fairy at Fairy Spring, on the Fairy Spring trail to Monta Rosa.
Bill, hanging up.
Big garnet outcrop, Warrensburg, NY.
Folded quartzite beds.
On the hike down we found another part of the Billings Fold, ~200 m along the axial surface.
Coming down from the summit. It’s actually not as steep as it looks.
Mylonite zone cutting gabbroic anorthosite, Keene Valley.
Salamander escapes from tent caterpillar.
Walloomsac metamorphosed calcareous sandstone, Rt. 8, North Adams, MA.
Metamorphosed tonalitic intrusives of the Taconian arc complex, Shelburne Falls, MA.
Large plagioclase megacryst in anorthosite, Mt. Jo.
Woodchuck on Jurassic red bed sediments, Turners Falls, MA.
Summit of Mt. Jo.
Large plagioclase crystal in Mt. Marcy-type anorthosite, Mt. Jo, short trail up.
Looking at leuconorite, cut by numerous ferrosyenite dikes that form an extremely block-rich intrusion breccia.
Brian pops out of the boulder cave.
Even more lunch.
Approaching the summit region.
Reaching the top of Mt. Jo, high peaks in the distance.
Same as above, with Mike and Bill for scale.
Bill reading the paper.
Eroded lamprophyre dike, near the summit of Mt. Jo.
Folded calc-silicate layer in marble, banks of the Hudson River.
Nick eating the finest peanut butter sandwich in New Hampshire.
Deformed xenolith breccia in gabbroic rocks, as part of the older plutonic complex in the roots of the Taconian island arc. Shelburne Falls.
Isoclinally folded quartzite beds.
Layer truncations against a thick quartzite. Possible pre-metamorphic sedimentary structures, or a fault surface.
Large metamorphic garnets in an amphibolite.
Searching for blue calcite, cascade slide.
Natural Bridge, in Natural Bridge State Park, North Adams, MA.
Coticule layer near the Billings Fold.
Well, it beats PB and J again.
Large xenolith choking the interior of a thin tourmaline granite sill.
Patrick pops out of the boulder cave.
Lunch on Black Precipice, sitting on the “Seven Sisters” quartzite beds.
Salamander rushes off at top speed.
Deformed marble with numerous ‘xenolith’ blocks and folded layers, Paradox.
Looking for graphite in marble, Warrensburg, NY.
Nick and Bill hanging out.
Crossing Roaring Brook on the way to some outcrops, Giant Mountain, Adirondacks.
Jeremy on Littleton Schist, with large sillimanite pseudomorphs after andalusite on the rock surface to the right.
More isoclinally folded quartzite beds.
Lunch on Black Precipice. Garnet- and tourmaline-bearing granite dikes and sills visible in the schist.
Large quartz mass in the neck between two large amphibolite boudins in marble, Paradox.
Metamorphosed tonalitic intrusives of the Taconian arc complex, Shelburne Falls, MA.
Pre-hike lunch making. Nothing better than peanut butter and jelly!
Alkali basalt dike cutting leuconorite, on the long trail down from the summit of Mt. Jo.
Large plagioclase crystal in a block of anorthosite within the leuconorite, summit of Mt. Jo.
View to the southwest, overlooking Monta Rosa.
Intrusion breccias and other intrusive features in the roots of the Taconic island arc, Shelburn Falls, Massachusetts.
Off the trail looking at complex isoclinal folds and graded quartzite beds.
Summit of Monta Rosa, with tourmaline veins, garnets, andalumps, and sillimanite fibers.
“Billings Fold” near the Monadnock summit.
Tonalitic gneisses and amphibolites at the Shelburne Falls, Shelburne Falls, Massachusetts.
Another group photo at Pine Cobble, Williamstown, Massachusetts. Stop 4 at 9:00 AM. Photo donated by Ralf Schauer.
Graded quartzite bed, stratigraphic top to the upper right.
The two notches in the outcrop are weathered out alkali basalt (camptonite?) dikes cutting leuconorite, near the summit of Mt. Jo.
View to the east from the summit. Boston was not visible today.
The largest plagioclase crystal found in this trip, larger than a size 12 boot.
Summit of Mt. Jo.
Hornblende needles in muscovite-biotite-chlorite-garnet schist.
Anna pops out of the boulder cave.
Infold of marble and calc-silicate layers into a partially separated amphibolite boudin neck, banks of the Hudson River.
The “Billings Fold”, a large isoclinal syncline just below and southwest of the Monadnock summit.
Checking out an especially large muscovite crystal in a pegmatite dike.
Large tourmaline crystals in a quartz vein. Longest crystal is ~4 cm.
Silurian Clough quartzite, Crag Mountain, just west of the Connecticut River valley.
Graded quartzite beds in Littleton Formation schist. Person is standing on the axial surface of an isoclinal fold that repeats the bed, upside down in front and right side up behind.
Hornblende-diopside-plagioclase-calcite vein in an amphibolite ‘xenolith’ in the deformed marble, banks of the Hudson River.
Late quartz vein with 25 cm wide tourmalinized zone around the vein.
Nice red garnets. The schists contain red garnets up to 2 cm across.
Looking at a quartz-pebble conglomerate in the Cheshire Quartzite, about half way up the trail to Pine Cobble, Williamstown.
If you are going to take a snooze, it might as well be in a nice spot!
“Billings Fold” just below the summit.
Feeling for fault movement indicators on a slickensided surface, Waloomsac Formation, Rt. 8, North Adams, Massachusetts.
Snoozing on the flysch and chips outcrop, eastern Berkshires, Massachusetts.
Looking closely at the corona textures and the green plagioclase flow foliation in a corona gabbro, near Schroon Lake.