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Appendix

Nomenclature of Common Metamorphic Rocks

Magmatic rocks are usually named after some locality. Only in rare cases does the name give any indication about the fabric and min­ eralogical composition of the rock. The names of magmatic rocks have to be memorized like words of a foreign language. Fortunately, this dif­ ficulty is not encountered in the nomenclature of most metamorphic rocks. It is only necessary to leam a few names of rock groups, which are characterized by a certain fabric andJor mineralogical composition. Furthermore, the presence of the main or critical is indicated by placing their names in front of the group name. For instance, there is the group of marbles, all of which contain well-crystallized carbonates as their main constituent. A particular marble may be designated as dolomite marble, -grossularite marble, marble, etc. Thus, the nomenclature of most metamorphic rocks is clear and easily understood. A more elaborate nomenclature based on quantitative mineralogical composition was proposed by Austrian petrographers after a discussion with colleagues from other countries. 1 This nomenclature is recommend­ able and is to a large extent adopted here.

Names of Important Rock Groups

Phyllite. Fine-grained and very finely schistose rock, the platy min­ erals of which consist mainly of phengite. Phengite sericite gives an overall silky sheen to the schistosity planes. The grain size is coarser than in but finer than in .

'''Ein Vorschlag zur quantitativen und qualitativen Klassifikation der kristallinen Schiefer" (a symposium). Neues Jahrb. Minerals Monatsh.: 163-172 (1962). Nomenclature of Common Metamorphic Rocks 341

In the amount of phyllosilicates (phengite + some chlorite ± ) exceeds 50%. The other most abundant constituent is . If the amount of quartz exceeds the amount of phyllosilicates, the rock is called a quartz . In both phyllites and quartz phyllites, albite may amount to as much as 20%. An exact designation of the rock is achieved by placing the name of subordinate constituents in front of the rock name, beginning with that present in the smallest amount. Minerals constituting less than 5% of the rock are generally not taken into consideration. Examples are -chlorite-albite phyllite and phlogopite-calcite phyllite. If amounts smaller than 5% are considered significant this can be desig­ nated by using an adjective form such as "-bearing." Schists. Medium- to coarse-grained rock, the fabric of which is characterized by an excellent parallelism of planar and/or linear fabric elements (schistosity). The individual mineral grains can be recognized megascopically (in contrast to phyllites). If mica, chlorite, tremolite, , etc., constitute more than 50% of a rock, the corresponding rock is called a mica , chlorite schist, tremolite schist, talc schist, etc. Phengite--chlorite-albite schists are known as . If aschist contains more quartz relative to the sum of the phyllosil­ icates, the rock is called quartz-mica schist. A further subdivision of schists is effected according to the same rules as in the case of phyllites. The cited symposium gives 20% as the maximum amount of feld­ spar in aschist. If rocks contain more , they are designated as rather than schists. It is true that schists commonly contain less than 20% and gneis ses more than 20% feldspar, but this distinction is generally not valid. The most characteristic difference between schists (or quartz schists) and gneis ses is not the mineralogie al composition but the fabric. This distinction between schistose and gneissic fabric was c1early stated by Wenk (1963): "When hit with a hammer, rocks having aschistose fabric (schists) split perfectly parallel to 's' into plates, 1-10 mm in thickness, or parallel to the lineation into thin pencil-like col­ umns." Schists split into thinner plates than gneisses. . Medium- to coarse-grained rock having a gneissic fabric, i.e., it "splits parallel to 's' generally along mica or layers, into plates and angular blocks, a few centimeters to tens of centimeters in thickness, or parallel to B into cylindrical bodies (pencil gneisses). The prevalent light-colored constituents (feldspar + quartz) have inter­ locking boundaries and provide, as compared to schists, a better coher­ ence and a coarser fissility to the rock; nevertheless, the fissility in many cases creates an almost perfect plane" (Wenk, 1963). Some prefer a def­ inition of gneiss based not only on fabric but also on mineralogica~ fea­ tures. Thus Fritsch et al. (1967) advocated the use ofthe term gneiss for 342 Petrogenesis of Metamorphic Rocks a rock with recognizable parallel structure consisting predominently of quartz and feldspar-feldspar amounting commonly to more than 20% and mica to at least 10%. Tw~ groups of gneisses are recognized. Orthogneisses are formed from magmatic rocks, such as granites, syenites, diorites, etc. On the other hand, paragneisses are derived from sediments, such as gray­ wackes, , etc. The particular mineralogical composition is indi­ cated according to the same rule as in the case ofphyllites, e.g., ­ --biotite gneiss. . A rock consisting predominantly of hornblende and plagioc1ase, which is produced by of basaltic magmatic rocks, tuffs, or marls. The hornblende prisms lie within the plane of schistosity ifthis is developed. The fissility generally is not as well devel­ oped as in schists. contain only small amounts of quartz or none at all. Marble. A rock consisting predominantly of fine- to coarse-grained recrystallized calcite and/or dolomite. Other minerals present are indi­ cated in the usual manner, e.g., -biotite marble. . A rock composed of more than 80% quartz. The inter­ locking boundaries of the quartz grains impart a great strength to the rock. Metamorphic must be distinguished from unmetamor­ phosed, diagenetically formed quartzites. Fels. Fels is a term referring to massive metamorphic rocks lacking schistosity, e.g., quartz-albite fels, plagioc1ase fels, calc-silicate fels. Generally, in English books, the term "rock" is used for such metamor­ phic rocks, e.g., lime-silicate rock (Harker, 1932, 1939). It is suggested that "fels" be used instead. . Nonschistose and fine-grained rock, which splinters on impact. The edges of thin rock chips occasionally are translucent like horn. The rock has a granoblastic fabric, i.e., it is a mosaic of equidi­ mensional small mineral grains, in which larger porphyroblastic minerals (or reHcs) are frequently embedded. are typically produced by contact metamorphism of clays, fine-grained graywackes, etc., and occasionally by regional metamorphism. , Granolite, and Granoblastite. See p. 256ff. Eclogite. See p. 276.

Prefixes

Meta-. This prefix designates metamorphosed igneous or sedimen­ tary roeks in which the original fabrie still can be reeognized; e.g., meta­ , metagraywackes. Others use the prefix "meta-" in a more gen- Nomenclature of Common Metamorphic Rocks 343 eral sense to designate metamorphic rocks according to the type of original rock from which they are derived. Example: Meta-graywacke or metadiorite = rock derived from graywacke or diorite. Ortho-. This prefix indicates that the originated from a magmatic rock, e.g., orthogneiss, orthoamphibolite. Para-. This prefix indicates that the metamorphic rock originated from a sedimentary rock, e.g., paragneiss, para-amphibolite.

Classification

A quantitative c1assification of common metamorphic rocks is shown in Figures A-l and A-2 taken with slight modification from the cited symposium (1962). The objections of Wenk regarding the distinc­ tion between gneiss and schist or phyllite should not be ignored; there­ fore, the boundary between the two groups, shown as a broken line in the two figures at 20% feldspar , should not be taken as critical in assign­ ing a name to a rock. The distinction between gneiss and schist or phyl­ lite is not based on mineralogical composition but on the character of fissility. This distinction is particularly significant if the mineralogical composition is the same. The c1assification shown in Figures A-l and A-2 applies to rocks predominantly composed of either quartz, , and phyllosilicates, or quartz, phyllosilicates, and carbonates. In many metamorphic rocks, these minerals are the main constituents. Figure A-2 is valid for rocks of

Albit, (Microclin.) S.ricit, (Biotit,. Chlorit.)

Fig. A-l Composition of metamorphic rocks of lower temperature ranges in terms of certain main constituents as indicated in the diagram. 344 Petrogenesis of Metamorphic Rocks

Muscolfit •• Biotit.

Fig. A-2 Composition of metamorphic rocks of higher temperature ranges in terms of certain main constituents as indicated in the diagram. lower temperature and Figure A-2 for rocks formed at higher tempera­ ture. In higher-grade metamorphic rocks, schists take the place of phyl­ lites, and calc-silicates such as diopside and grossularite, which are not found in rocks oflow temperature, are present, e.g., in marbles (silicate marble). The names of most metamorphic rocks consist of compound terms:

a. A combination of the names of constituent minerals; b. A name for the category of rock according to its fabric, such as phyllite, gneiss, schist, fels.

Commonly, rocks with the fabric characteristics of gneiss, schist, etc., are formed in the appropriate field of mineralogical compositions as given in the preceding figures, but this is not invariably so. In any case, the name gneiss, schist, etc. is to be used only ifthe characteristic fabric is developed, irrespective of mineralogical composition.

References

Fritsch, W. Meixner, H., and Wieseneder, H. 1967. Neues Jahrb. Mineral. Monatsh. 1967: 364-376. Harker, A. 1932, 1939. Metamorphism. Methuen, London. Wenk, C. 1963. Neues Jahrb. Mineral. Monatsh. 1963: 97-107. Index

ACF Diagram, 35ff, 44ff, 17lff Aragonite, 175ff, 179f, 190, 193, 195, Acmite, 177, 179, 194,205,276 198f, 205, 240f Actinolite, 40, 71ff, 152, 17lff, 174ff, 178, 184, 189ff, 195ff, 212, 24Of, , metamorphism of, 169ff 244,280 Biotite, 41, 43f, 5lff, 85f, 98,147,169, Adularia, 187f 173, 21lff, 215ff, 219ff, 223, , See Acmite 227ff, 23Off, 234, 242f, 264ff, AFK Diagram, 39, 42ff 268ff, 273, 284, 286, 310, 313, AFM Diagram, 48ff 316, 32Off, 337 Äkermanite, 136ff Bronzite, 264f Albite, 12,45,75, 89f, 150, 169f, 171ff, , 127f, 13lf, 154ff, 164f,244f, 178ff, 187ff, 204, 207, 211, 228, 253 241,244,280 Burial metamorphism, 4ff, 6 Alkali feldspar , See K feldspar Allochemical, See Metasomatic , 41, 5lf, 76, 78, 82, 85, 9Off, Calcite, 34, 70, 112ff, 126ff, 128ff, 169, 17lff, 217f, 22Off, 224f, 134ff, l4Off, 147ff, 170, 176f, 227ff, 23Off, 233ff, 244f, 250, 260, 185f, 19Of, 200f, 205, 210, 212, 264ff, 270, 277, 28Of, 284, 316, 241, 248ff, 264, 286 32lf,323 Carbonate rocks, metamorphism of, 19f, Amphibolite, 168ff, 173, 342 11lff Amphibolite facies, 64ff, 75ff Cataclastic metamorphism, 2 Analcime, 9, 12, 188ff Chabazite, 188 Anatexis, 8,65, 85f, 23Of, 251, 283ff, Charnockitic granolite, 263f 286ff, 309ff, 316ff, 329ff Chlorite, 9, 11,41, 5lf, 7Off, 74ff, 82, Andalusite, 40, 78, 82, 90, 9lff, 147, 99, 14Of, 147, 162f, 169, 17lff, 209f, 218, 227, 230, 246ff, 253 18lff, 184ff, 189ff, 195ff, 207, Andesite, metamorphism of, 168ff 21Of, 215ff, 219ff, 223, 227f, , 40, 264, 280f 24Off,244ff Anhydrite, 2 Chloritoid, 40, 5lf, 73, 76ff, 107f, 141, Ankerite, 219 147, 215ff, 218ff, 22Off, 223, 227, Annite, 51 245f,280 Anorthite, 40, 45, 142ff, 147ff, 248, Chondrodite, 127 285. See also Plagioclase Chrysotile, 154ff, 159ff , 41, 154ff, 161, 250, 253f Clays, metamorphism of, 205ff Antigorite, 154ff, 159ff, 244f. See also Clinochlore, 127f, 152 Serpentine Clinohumite, 127 346 Petrogenesis of Metamorphic Rocks C1inoptilolite, 9, 187f, 197. See also Gismondine, 188 Glauconite, 9, 211f Clinopyroxene, See Diopside Glaucophane, 5, 11, 41, 65, 73, 89f, Clinozoisite, See Zoisite 175ff, 179, 194f, 198f, 205, 24Of, Coalification, 2, 13 276,280 Contact metamorphism, 2ff, 97ff, 133ff, Gmelinite, 188 252f Gneiss, nomenclature, 341f Cordierite, 40, 77ff, 82f, 85, 91ff, 99, Grade of metamorphism, 6ff, 64ff, 239ff 221ff, 223ff, 229, 23Off, 233ff, Granite, 281ff, 283ff, 307, 31Off, 314, 245ff, 250, 252f, 27Off, 284, 286, 316ff,320,323ff,329ff,333ff 316,321,323 Granitization, 285, 325, 329, 33Of, 332f , 142 Granoblastite, 258f, 264ff Crossite, 41, 175ff, 194 Granoblastic texture, 258f, 261f Cummingtonite, 40, 161, 172f Granolite, Definition etc., 259ff, 264ff, 280f Diagenesis, 1, 5, 8, 9ff, 188f, 207 Granulite, 54, 88, 168, 234, 256ff. See Diaphtoresis, 17 also Granolite Differentiation, metamorphic, 17 Graphite, 19ff, 22f, 141,147,209 Diopside, 40,98, l06f, 113ff, 131, 136f, Graywacke, metamorphism of, 204f, 152, 163ff, 169ff, 187, 264, 267ff, 268, 309ff, 326ff 276 , Greenstone, 170ff Dolomite, 40, 112ff, 125ff, 132, 140, Greenschist facies, 64f, 74f 147, 154, 164, 210, 219, 249, 264 Grossularite, 40, 142ff, 152, 193, 220, Dynamothennal metamorphism. 3ff 248, 264, 266f, 277, 280f Grunerite, 40 Eastonite-Siderophyllite, 52 Eclogite, 88, 165, 268, 276ff Hedenbergite, 40, 276 Enderbitic granolite, 263f , 24f, 2i7 , 41, 154ff, 161ff Heulandite, 9, 13, 184ff, 187, 189 Epidote, 40, 7Of, 152, 169, 173, 175ff, Hornblende, 40, 75f, 163, 169ff, 174, 178f, 183, 189, 191ff, 196ff, 212, 244f, 252, 260, 264ff, 273, 276, 219f, 242, 276, 280. See also 279, 284, 316, 322f, 337 Zoisite Hornfels, Hornfelsfacies, 2, 57ff, 99, Eutectic, 291 252, 347 Evaporites, 2 Hydrothermal metamorphism, 2f Hypersthene, 41, 88, 252f, 256ff, 260, Facies, general, 55ff 264ff, 272f, 276 Fluid phase, 15ff, 19ff, I11ff Hypersthene zone, 87f, 170,234, 256ff Forsterite, 113ff, 132, 136f, 155ff, 16Off, 243, 245, 249f, 253 Idocrase, 40, 151f Fugacity, fugacity, 24ff Illite, 9, 11, 13, 72f, 206f, 210 Ilmenite, 322 Gamet, See Almandine Isochemical, 16ff Gedrite, 41, 322 , 66ff Geobarometer, 148,.151,246,248, 25Off, 254, 272 Jadeite, jadeitic , 5,41,65,69, Geothermometer, 114,246, 25Off, 272, 73,89f, 176f, 190, 194, 198f, 204f, 281 24Of, 276f, 281 Index 347 Kaolinite, 11, 14Of, 146, 200, 206ff, 210 Muscovite, 23, 41, 43f, 76ff, 81, 83ff, K feldspar (including alkali feldspar) , 43, 86ff, 99, 147, 149, 172,207,211, 53, 83ff, 99, 149f, 206, 211ff, 219ff, 223, 227ff, 231, 242f, 245f, 214ff, 218ff, 23Off, 250, 252f, 260, 249f, 264, 280 265ff, 269ff, 286ff, 290, 309ff, 316 , 2 Kyanite, 40, 78, 82ff, 90, 91ff, 147f, 209ff, 218, 227, 246ff, 253, 270, Natrolite, 188 272, 276f, 279 Nontronite, 185

Larnite, 134ff , See Forsterite Laumontite, 2, 5f, I1ff, 40, 65, 89f, 140, Omphacite, 276, 281 175ff, 180, 182f, 184f, 186ff, 197f, Orthopyroxene. See Enstatite, Bronzite, 200, 240ff and Hypersthene , 5, I1f, 40, 65, 68ff, 72, 89f, 140, 175ff, 189ff, 191f, 195f, 198, Paragenesis, general, 28ff 200, 204f, 240ff Paragonite, 11,41, 43f, 69, 14Of, 147, Levyne, 188 151,176,200,207, 21Of, 253, 280 Lizardite, 154 , metamorphism of, 206ff, 268ff Periclase, 131ff, 136, 155ff Mafic rocks, metamorphism of, 168ff Phase Rule, 19,32, 113 Magnesite, ll1ff, 126, 131f, 154ff, Phengite, 11,41,43, 72f, 140,207, 162ff 21Off, 219f, 242, 34Of. See also Magnetite, 23f, 154, 166,217,223, 322 Muscovite Margarite, 40, 69f, 141, 146ff, 150,210, Phillipsite, 188 246ff Phlogopite, 41, 52, 116, 127f, 163 Mariolite, 40 Phyllite, nomenclature, 340f MarI, metamorphism of, 14Off, 200 Pistacite, 40, 71 Mejonite, 40 Plagioclase, 75f, 83ff, 86, 107f, 143, Melilite, 133, 136 147ff, 169ff, 244, 250, 260, 264ff, Merwinite, 133, 136f 277, 286ff, 316, 319ff. See also Mesolite, 188 Albite and Anorthite Metamorphism Prehnite, 11, 40, 65, 68, 72ff, 90, 140, Beginning of, llf 175, 179ff, 181ff, 189ff, 193, 196f, Definition, If, 8 200, 204f, 240ff Dynamothermal, 3ff Pressure Factors of, 15ff Directed, 24f Hydrothermal, 2ff, 184ff Fluid, 18ff Retrograde, 2, 17 Hydrostatic, 18 Types, Iff, 6f Load, 18f Metamorphic grades. See Grades of Overpressure, 18, 25f metamorphism Solid, 19 Metasomatism, 16f, 329, 331f Units, 18 , 8, 83, 104, 246, 250, 264, Pressure divisions of metamorphic 283ff, 323, 325ff grades, 88ff Monticellite, 133, 136 Pumpellyite, 40, 65, 68ff, 90, 175f, Montmorillonite, 9, 11, 200, 206f, 210 18lff, 189ff, 196ff, 200f, 204f, Mordenite, 186, 188 240ff 348 Petrogenesis of Metamorphic Rocks Pyrope, 41, 163,220,260,266,277, Staurolite, 4Of, 5If, 76ff, 8If, 99, 103ff, 280f 211,219, 22Iff, 228ff, 247, 249, , 11, 40, 73, 14Of, 147, 253ff 200f, 206ff, 210, 215ff, 218 Stilbite, 188, 197 Stilpnomelane, 41, 44, 5If, 173f, 176ff, Quartz. Too many to be cited here 181,205, 211ff, 219, 242f

Tale, 41, llIff, 154ff, 24Of, 250, 253, Rankinite, 134ff 254 Reaction-isograd, 66ff Thomsonite, 188 Regional metamorphism, 3ff, 102ff Tilleyite, 134ff , 179, 212 Tremolite, 40, 98, 107f, 112ff, 152, , 109, 201, 276 163ff,249

Sagvandite, 154 Ultramafic rocks, metamorphism of, Sanidinite facies, 133ff 154ff Sapphirine, 163, 272f , 40, 127, 264 Vesuvianite. See Idocrase Schist, nomenclature, 341 Scolecite, 188 Wairakite, 89, 181, 183, 184ff, 192, Serpentine, 154ff, 163ff, 24Of, 243, 253 196f, 200 , 40, 83ff, 9Iff, 103ff, 227f, Wollastonite, 19,29,40,98, 126, 128ff, 23Off, 234ff, 250, 253, 265, 270, 134ff, 142ff, 146, 252 272,286,316,32Off Spessartine, 41, 220, 231, 260, 280 Zeolite facies, 5, 184ff, 200 Sphene, 169ff, 176ff, 182, 201, 205, Zoisite, inclusive Orthozoisite and 322 Clinozoisite, 40, 68ff, 74f, 82, 90, Spilite, 197 141ff, 145ff, 148ff, 151, 169, Spinei, 127, 163 17Iff, 175f, 181, 189ff, 210, 24Off, Spurrite, 133ff 247f, 253, 266, 276, 279