Petrology: The (almost) forgotten art of hand drawings in petrology

Here are some sets of drawings that I did for a variety of projects a long time ago. Note that the artwork is rather crude, and some of the labels, captions, and even the spelling exhibit a somewhat primitive understanding of petrology and English. Nonetheless, I hope you gather that drawings can frequently offer insight of a process or views that are difficult to capture with a photo or computer-rendered illustration.

Figures done in the 1977 Petrology class with Peter Robinson, University of Massachusetts, Amherst, Hawaii suite

Typical mineral relations, olivine phenocryst rimmed by augite.

HW-2A. Hawaii alkali basalt.

Dehydration reaction rim around basaltic hornblende. B is hornblende, pinkish-brown is titanian augite, most opaques are actually dark-blown.

HW-2A. Hawaii alkali basalt.

Typical textural relations in HW-2C. The groundmass is mainly plagioclase, augite, olivine, magnetite, and void space.

HW-2C. Hawaii alkali olivine basalt.

Typical euhedral olivine in groundmass.

HW-3. Hawaii olivine basalt.

Typical euhedral augite crystal, and optic orientation diagram.

HW-3. Hawaii olivine basalt.

Phenocrysts and microphenocrysts in a microcrystyalline groundmass.

HW-8A. Hawaii olivine basalt.

Typical mineral relations. Note minor resorption of olivine and augite.

HW-8B. Hawaii olivine basalt.

Morphology of opaque minerals in the slide. O is an olivine grain being resorbed by magma, with opaques on its surface. Other minerals not shown.

HW-9B. Hawaii olivine basalt.

Monoclinic isosanidine core inside of isosanidine, surrounded by colorless glass, and with some small plagioclase crystallites.

HW-11A. Hawaii trachyte obsidian.

p.s. I don’t think isosanidine is a real thing.

Figures done in the 1977 Petrology class with Peter Robinson, University of Massachusetts, Amherst, Salem suite

Typical mineral relations. Note alteration of remnant clinopyroxene to grunerite, with ferrohastingsite. p.s. The clinopyroxene is probably olivine.

SA-4A. Alkali fayalite granite. No fayalite here, though.

Typical mineral relations. Note alteration of fayalite to limonite and grunerite, grunerite to biotite, hedenbergite to ferrohastingsite, and ferrohastingsite to blue-green soda amphibole. Also note radiation halos around zircon and allanite (probably chevkinite).

SA-4B. Alkali fayalite granite. Here is fayalite.

Typical mineral relations in granite. Note the alteration of fayalite to grunerite, grunerite to biotite, and hedenbergite to ferrohastingsite.

SA-4D. Alkali fayalite granite. More fayalite.

Typical mineral relations in the mafic dike. Note alteration of opaque mineral to sphene.

SA-4D. Basalt dike cutting granite, metamorphosed by cooling in contact with hot granite.

Typical mineral relations. Hedenbergite is altering to ferrohastingsite and biotite, and the hedenbergite is in turn altering to a colorless amphibole. Perthite is in part altered to sericite, and opaques in part to sphene. Note interstitial quartz.

SA-5. Hedenbergite granite.

Interstitial ferrohastingsite with apatite and perthite.

SA-6B. Alkali granite.

Biotite crystal with hematite intergrowths, probably breakdown products of amphibole.

SA-6B. Alkali granite.

Figures done in the 1977 Petrology class with Peter Robinson, University of Massachusetts, Amherst, assorted rocks

Typical mineral relations. Note filling of crack in garnet with clinozoisite and calcite.

7Q5. Amphibolite facies calc-silicate rock. Not very colorful, except in cross-polarized light.

Typical mineral relations. Note alteration of opaque mineral (ilmenite) to a nearly opaque pseudomorph (leucoxene?), and ankerite to limonite. Also note sharp, unreacting contact between chloritoid and chlorite.

CHL. Greenschist facies chloritoid-chlorite-muscovite schist.

Typical mineral relations. Note alteration of plagioclase to calcite and epidote, and the planes of fluid inclusions in apatite.

Elizabethtown, NY. Two-pyroxene granulite (only one pyroxene illustrated here).

Typical mineral relations. Note alteration of colorless ferromagnesian minerals to hornblende, and plagioclase to epidote and sericite.

O5F8. Amphibolite facies calc-silicate rock.

p.s. Sphene forever!

Typical mineral relations. Note zoned garnet and slight alteration of garnet to chlorite and opaques.

UO1B. Amphibolite facies pelitic schist.

Masters thesis illustrations on retrograded pelitic schists, New Salem area, Massachusetts

Fibrolite textures in thin section. a) Littleton Formation. A large bundle of sillimanite rods and fibers partially replaced by fine-grained muscovite, characteristic of sillimanite in zone Rl. b) An example of sillimanite in zones R2 to R4, where it occurs only as tiny rods within single quartz crystals.

Sillimanite in slightly and severely retrograded schists.

Drawings of garnets from various samples. The sequence from a to d shows the concentric manner of garnet alteration. These are pictures a and b.

Garnet in two slightly retrograded rocks, first two examples.

Drawings of garnets from various samples. The sequence from a to d shows the concentric manner of garnet alteration. These are pictures c and d.

Garnet in two severely retrograded rocks, second two examples.

Textures of staurolite in thin section. a) Station UOIA, zone R2. Fresh staurolite with abundant quartz and graphite inclusions and well-formed mica plates in the matrix. b) Station NS111, zone R4. Pseudomorph after staurolite composed largely of muscovite and chlorite. Note the outline and shading of the pseudomorph core by abundant graphite particals, and recrystallization of some muscovite into larger, oriented plates.

Fresh vs. retrograded and completely pseudomorphed staurolite.

Garnet partly transformed to chlorite, and some ilmenite partly transformed to anatase. Chloritoid in the matrix,

Partly retrograded garnet, with retrograde chloritoid. See illustration below.

Composite drawing showing habit of chloritoid in sample NS7l. As shown, chloritoid may occur in various orientations with respect to the main foliation, and is rife with quartz inclusions. Cleavage cracks on 001 and 110 are commonly displayed. Note that chlorite and muscovite are common, but biotite and feldspar do not occur with chloritoid. Ilmenite is partially altered to anatase.

Chloritoid in partially retrograded schist, also showing ilmenite partly retrograded to anatase.

Biotite in an early stage of replacment by muscovite and chlorite. Note the ilmenite platelets, probably derived from titanium released from biotite. This example contains K-feldspar lenses within the biotite.

Partially retrograded biotite containing lenses of retrograde K-feldspar. The blurry but apparently small 2V of the K-feldspar suggests it is sanadine.

Drawings of ilmenite in thin section. a) Large, thick ilmenite plates of prograde origin, parallel to the foliation. Note quartz inclusions. b) Drawing of ilmenite in reflected light, showing the abundant rounded quartz inclusions. c) Large, thin, tapered ilmenite plates of prograde origin. Ilmenite is partially altered to anatase, and is severely deformed in crenulation folds. d) Small ilmenite plates of retrograde origin. precipitated from titanium released from altering biotite. Also present is a large grain of prograde origin.

Prograde ilmenite and retrograde anatase in transmitted (left) and reflected (right) light.

Composite drawing showing textural relationships between sphene, the oxides, and silicates. Note the euhedral outline and hint of concentric zoning on the sphene grain to the lower left. Parts of that grain are altered to leucoxene, doubtless a weathering product.

Sphene, ilmenite, and anatase, plus analytical data.

In case you forgot: Sphene forever!

Spots on garnet analyzed by electron microprobe, from Hollocher, 1987

Analysis spots on some fresh and retrograded garnets.

Several garnets showing garnets in various states of retrograding in various relationships to chlorite.

Sketches made for research paper summaries, Volcanology class taught by J.M. Rhodes and Marty Godchaux

Summary sketch of the stratigraphy in the sampling area for Mt. Rainier ash beds. This shows interlayered ash beds and coarse fluvial deposits, with buried forests which gave age control from carbon 14 dating.

Ash beds in the Mt. Rainier area.

This was about geologic freeboard, which is the height of the surface relative to sea level. I think here is showing thick, buoyant continental crust standing higher than thin, dense oceanic crust.

Volcano top elevations, original point unclear to me.

I think this is showing that the elevation of volcano tops is determined by the depths to the magma chambers feeding the volcanoes. The idea here is that the magma chamber-volcano top elevation difference is always the same. I suspect this is a hypothetical that was discussed in the paper.

Volcano top elevations based on magma chamber depths.

Sketches made for some 1980’s field trip guidebooks

outcrops along the road, showing amphibolites and solidified veins and dikes of tonalitic partial melts from those very same amphibolites. Melting was driven by cummingtonite dehydration.

Orthopyroxene tonalite partial melts in amphibolite, Rt. 9, Belchertown, Massachusetts.

Tonalite melt veins in dioritic two-pyroxene granulite. Melts were probably from this very rock, driven by hornblende dehydration.

In-situ melt veins in two-pyroxene granulite, Masapaug Rd. near Sturbridge, MA.

Slides for a presentation on retrograde metamorphism, M.S. thesis, circa 1979 (back when I had a sense of humor)

Hypothetical graphs showing two possibilities for the New Salem retrograde area in Massachusetts: retrograding during cooling from prograde metamorphism, or a separate prograde heating event to moderate temperatures.

Retrograde metamorphism: during cooling or or more complex polymetamorphism.

Phase diagrams showing schematic retrograde sillimanite-out reaction.

Retrograde sillimanite-out reaction.

Phase diagrams showing schematic retrograde staurolite-out reaction.

Retrograde staurolite-out reaction.

Phase diagrams showing schematic retrograde chloritoid-in reaction.

Retrograde chloritoid-in reaction.

Phase diagrams showing schematic retrograde staurolite-out reaction.

Hypothetical retrograde reaction removing staurolite.

Phase diagrams showing a continuation of the schematic retrograde staurolite-out reaction.

Retrograde hypothetical reaction.

Phase diagrams showing the final schematic for the retrograde staurolite-out reaction.

Retrograde hypothetical reaction, terminal for staurolite in this system.

Phase diagrams showing schematic for the retrograde garnet-out reaction.

Retrograde garnet-out reaction progression.

Phase diagrams showing schematic for the retrograde garnet-out reaction, terminal for garnet in this system.

Retrograde garnet-out reaction.

Cartoon chlorite pseudomorph after garnet.

Sans gloves, chlorite pseudomorphs after garnet actually look rather like this.

Perspective drawing showing how a muscovite projection works in the AKFM system.

Muscovite projection explanation.

AKFM projection from muscovite onto the AFM plane.

Muscovite projection result.

Prograde phase relations as seen in muscovite projection.

Prograde phase relations.

AKFM ternary system, viewed down the FM edge.

Edgewise view of the AKFM tetrahedron.

AKFM ternary system, viewed down the FM edge, showing the retrograde staurolite-out reaction.

Edgewise view of the AKFM tetrahedron showing the retrograde staurolite-out reaction.

AKFM ternary system, viewed down the FM edge, showing the retrograde garnet-out reaction.

Edgewise view of the AKFM tetrahedron showing the retrograde garnet-out reaction.

AKFM ternary system, viewed down the FM edge, showing the retrograde K-feldspar-in reaction.

Edgewise view of the AKFM tetrahedron showing the retrograde K-feldspar-in reaction.

One way to imagine how Mn and Ca stabilize garnets, so they can show up in many different assemblages in the AKFM system where they would not be expected in the pure Fe-Mg system.

One way to think of why garnets occur in so many assemblages.

A strange H2O-TiO2-Fe-O tetrahedral composition space. Probably not very helpful.

One way to look at oxide and silicate assemblages. Don’t take this too seriously.

Mr. Staurolite, walking down the street.

Well, haven’t you been wondering?