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Rock Identification For Blue Planet Class spring, 2007

Information and images gathered by 
Just to let you know, I took this class (above) in 2007 and don't remember much from the class. This identification list was something I made to help myself in class. If you want a classification of a certain stone that you have, go to a geology professor at your local university or college or take your rock to a lapidary shop.

Igneous   |   Sedimentary   |   Metamorphic

Aphanitic = can’t see grain except with microscope
phaneritic = can see sand to pea sized
pegmatitic = course; large grain dime, quarter & larger size.

Clastic rocks are rocks formed from fragments of pre-existing rock. The most common usage is for clastic or detrital sedimentary rocks. However, the usage is not restricted to sediments.
This was my study guide for use in my Blue Planet, Environmental Science Class. The numbers are from the rock samples and our Class list.

Igneous – Magmatic origin

40. Pumice

Made from ash, pyroclastic, loose crumbly, no mica.
Top stone is obsidian (black), below that is pumice and in lower right corner is rhyolite (light color)
Image:  Pumice
Pumice is a highly vesicular pyroclastic igneous rock of intermediate to siliceous magmas including rhyolite, trachyte and phonolite. Pumice is usually light in color ranging from white, yellowish, gray, gray brown, and a dull red. Pumice has an average porosity of 90%.
Pumice is formed as pyroclastic material is ejected into the air as a froth containing masses of gas bubbles or vesicles, the lava solidifies quickly and the vesicles are contained in the rock. The basaltic version of pumice is known as scoria and has
many differences due to mineralogy. 

More Pumice
Image:  pumiceImage:  pumice

41. Scoria

Like basalt with bubbles, frothy.
Image:  scoria

Scoria is the vesicular ejecta of basaltic and andesitic magmas. Generally a dark brownish black or red, scoria is generally thought of as the mafic version of pumice, forming when magma rich in dissolved gases is vented. Scoria is composed of volcanic glass fragments, and has few mineral crystals. Its specific gravity ranges from 0.8 to 2.1, making it a relatively light form of rock - sometimes light enough to float (at less than 1.0 specific gravity).

As the magma encounters lower pressures, the gases are able to escape and form vesicles. These vesicles are trapped when the magma cools and solidifies. Vesicles are usually small, spheroidal and do not impinge upon one another, instead they open into one another with little distortion. Volcanic cones of scoria can be left behind after eruptions, usually forming mountains with a crater at the summit. An example is Mount Wellington, Auckland in New Zealand , which like the Three Kings Mount in the south of the same city has been extensively quarried.

42. Basalt

Aphanitic, no quartz, low feldspar, high olivine.
Image: basalt
Image:  basalt
Basalt is a common gray to black volcanic rock. It is usually fine-grained due to rapid cooling of lava on the Earth's surface. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or gray.

43.  Rhyolite

aphanitic, quartz, feldspar, no olivine.
Image: rhyolite
Image:  rhyolite
Rhyolite is an igneous, volcanic (extrusive) rock, of felsic (acidic) composition (typically >69% SiO2 -- see the TAS classification. It may have any texture from aphanitic to porphyritic. The mineral assemblage is usually quartz, alkali feldspar and plagioclase (in a ratio > 1:2 -- see the QAPF diagram). Biotite and pyroxene are common accessory minerals.

44. Granite

Phaneritic, quartz, feldspar, no olivine.
Image: granite Image:  granite
Image:  granite quarry
Quarrying granite for the Mormon Temple, Utah Territory. The ground is strewn with boulders and detached masses of granite, which have either fallen or have been hewn from the walls of Cottonwood Canyon. The quarrying consists of splitting up the blocks.
A common and widely occurring type of intrusive, felsic, igneous rock. Granites are usually medium to coarse grained, occasionally with some individual crystals larger than the groundmass forming a rock known as porphyry. Granites can be pink to dark gray or even black, depending on their chemistry and mineralogy. Granite is nearly always massive, hard and tough, and it is for this reason it has gained widespread use as a construction stone.

45. Pegmatite

Pegmatitic, high quartz & Feldspar.
Image: pegmatite
Pegmatite with blue corundum crystals

Pegmatite is a very coarse-grained igneous rock that has a grain size of 20 mm or more; such rocks are referred to as pegmatitic.
Most pegmatites are composed of quartz, feldspar and mica; in essence a "granite". Rarer "intermediate" and "mafic" pegmatite containing amphibole, Ca-plagioclase feldspar, pyroxene and other minerals are known, found in recrystallised zones and apophyses associated with large layered intrusions.
Crystal size is the most striking feature of pegmatite, with crystals usually over 50mm in size. However, individual crystals over 10 meters across have been found, and the world's largest crystal was found within a pegmatite.


Image:  tufaImage: Tufa
Tufa is the name for an unusual geological form of calcite rock. Tufa is formed when water evaporates from lime-rich waters, leaving calcite (calcium carbonate) to crystallize, often with impurities of iron oxides (rust), which give tufa its yellow and red coloration.
Tufa is formed on cliffs, caves and quarry faces where limestone is naturally occuring. This rock can form very quickly if conditions are favourable. Plants, mosses and invertebrates oftem become encrusted in the calcite, and preserved as fossils.
Tufa is a rough, thick, rock-like calcium carbonate deposit that forms by precipitation from bodies of water with a high dissolved calcium content. Tufa is not to be confused with tuff which is volcanic.
Tufa deposition occurs in seven known ways:
Mechanical precipitation by wave action against the shore. This form of tufa can be useful for identifying the shoreline of extinct lakes (for example in the Lake Lahontan region).

  • Precipitation from supersaturated hot spring water entering cooler lake water.
  • Precipitation in lake bottom sediments which are fed by hot springs from below.
  • Precipitation from calcium-bearing spring water in an alkaline lake rich in carbonates.
  • Precipitation throughout the lake as the lake dries out.
  • Through the agency of algae. Microbial influence is often vital to tufa precipitation.
  • Precipitation from cold water springs (for example in the foothills of the Rocky Mountains near Hinton, Alberta)

There are some prominent towers of Tufa at Mono Lake and Trona Pinnacles in California, USA, formed by method 4, above. Tufa is also common in Armenia and central-southern Italy (Campania, Lazio and Tuscany).
Usage note: The rock type "tufa" is commonly confused in name by laypersons with the rock type "tuff", which is a rock formed from welded volcanic ash. These rocks are nothing like each other.

48. Tuff

Pyroclastic texture, Welded Ash
Image: tuff
Image:  tuff
Tuff (from the Italian "tufo") is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. (Note that tuff is a type of rock entirely different from tufa.)

49. Gabbro

Phaneritic, High olivine, low Feldspar, less quartz
Image:  gabro
Image:  gabro

Gabbro is a dark, coarse-grained, intrusive igneous rock chemically equivalent to basalt. It is a plutonic rock, formed when molten magma is trapped beneath the Earth's surface and cools into a crystalline mass.
The vast majority of the Earth's surface is underlain by gabbro within the oceanic crust, produced by basalt magmatism at mid-ocean ridges.
Gabbro is dense, greenish or dark-colored and contains varied percentages of pyroxene, plagioclase, amphibole, and olivine (olivine gabbro when olivine is present in large quantities) The pyroxene is mostly clinopyroxene, small amounts of orthopyroxene may be present

51. Obsidian

Pyroclastic texture, glassy, dark
Image: obsidian
Obsidian from Lake County, Oregon
Obsidian is a rock which is a type of naturally occurring glass, produced by volcanoes (igneous origin) when a felsic lava cools rapidly and freezes without sufficient time for crystal growth (see glass transition temperature). It is commonly found within the margins of felsic lava flows, where cooling is more rapid. Because of the lack of crystal structure, obsidian blade edges can reach almost molecular thinness, leading to its ancient use as arrowheads, and its modern use as surgical scalpel blades.
While a rock like basalt is dark because of ferromagnesian enrichment, obsidian consists mainly of SiO2 (silicon dioxide), usually 70% or more. Obsidian is mineral-like, but not a true mineral because it is not crystalline. Its composition is very similar to that of granite and rhyolite. It is sometimes classified as a mineraloid. Because obsidian is metastable at the earth's surface (over time the glass becomes fine-grained mineral crystals), no obsidian has been found that is older than Cretaceous age. The breakdown of obsidian is accelerated by the presence of water.
Image:  snowflake obsidian
Snowflake obsidian

Sedimentary – Secondary, made from igneous rocks broken down

54. Arkose

clastic, sand, round
Image: arkose
Arkose sandstone found in Slovakia
Image: arkose
Arkose is composed mainly of pink or white feldspar grains, with quartz, and generally some muscovite mica or sand-sized rock fragments
Arkose is a detrital sedimentary rock containing roughly 60% quartz sand and 25% feldspar, typically gray to reddish in color. The sand may range from fine to very coarse, but tends toward the coarser end of the scale. Arkose usually contains small amounts of calcite cement, which causes it to effervesce slightly in dilute hydrochloric acid; sometimes the cement also contains iron oxide. Similarly, arkosic sand is sand that is rich in weathered feldspar.
Arkose is generally formed from the weathering of granitic rocks, which are primarily composed of quartz and feldspar. Occasionally it contains fragments of mica from the parent rock. These sediments must be deposited rapidly and/or in an arid environment such that the feldspar will not undergo chemical weathering and decompose; therefore arkose is designated a texturally immature sedimentary rock. Common facies in which arkose is found include conglomerate deposits with granitic source rocks and above unconformities in granitic terrain.
Due to these necessities of the depositional process, fossils are rare in arkose, though bedding is frequently visible

55. fossiliferous limestone (fossils)

Evaporite, with fossils
Image: fossiliferous limestone
Image:  fossiliferous limestone
Limestone is a sedimentary rock composed largely of the mineral calcite (calcium carbonate: CaCO3). Limestone often contains variable amounts of silica in the form of chert or flint, as well as varying amounts of clay, silt and sand as disseminations, nodules, or layers within the rock. The primary source of the calcite in limestone is most commonly marine organisms. These organisms secrete shells that settle out of the water column and are deposited on ocean floors as pelagic ooze or alternatively is conglomerated in a coral reef (see lysocline for information on calcite dissolution). Secondary calcite may also be deposited by supersaturated meteoric waters (groundwater that precipitates the material in caves). This produces speleothems such as stalagmites and stalactites.

56. Coal (bituminous)

Image: coal
Image: coal
Bituminous coal is a relatively hard coal containing a tar-like substance called bitumen. It is of better quality than lignite coal but of poorer quality than anthracite coal.
Bituminous coal is an organic sedimentary rock formed by diagenetic and submetamorphic compression of peat bog material.
Bituminous coal has been compressed and heated so that its primary constituents are the macerals vitrinite, exinite, etc. The carbon content of bituminous coal is around 60-80%, the rest is composed of water, air, hydrogen, and sulphur which have not been driven off from the macerals.
The heat content of bituminous coal ranges from 21 to 30 million Btu/ton (24 to 35 MJ/kg) on a moist, mineral-matter-free basis.
Bituminous coal is usually black, sometimes dark brown, often with well-defined bands of bright and dull material. Bituminous coal seams are stratigraphically identified by the distinctive sequence of bright and dark bands and are classified accordingly as either "dull, bright-banded" or "bright, dull-banded" and so on.

57. Limestone (oolite)

Image: Limestone, oolite
Image: limestone, oolite
Image:  limestone, ooliteImage: limestone, oolite
Another form taken by calcite is that of oolites (oolitic limestone) which can be recognized by its granular appearance.

58. Limestone (Evaporite)

Image:  limestone, evaporite
Limestone makes up about 10% of the total volume of all sedimentary rocks.
Pure limestone is white or almost white. Because of impurities, such as clay, sand, organic remains, iron oxide and other materials, many limestones exhibit different colors, especially on weathered surfaces. Limestone may be crystalline, clastic, granular, or massive, depending on the method of formation. Crystals of calcite, quartz, dolomite or barite may line small cavities in the rock. Folk and Dunham classifications are used to describe limestones more precisely.

61. Conglomerate

clastic, gravel, round
Image:  conglomerate Image:  conglomerate Image:  conglomerate
A conglomerate with iron oxide cementing material
A conglomerate is a rock consisting of individual stones that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts. Both conglomerates and breccias are characterized by clasts larger than sand (>2 mm).

63. Breccia (not on test)

Clastic, course gravels, round, conglomerate.
Image:  breccia
Image: breccia image: breccia Image: breccia illustration
Breccia is typically a sedimentary rock composed of angular fragments from a previous rock structure, cemented in a matrix that may be of a similar or a different material. It is therefore a clastic rock.

64. Shale

Clay, flat flake, fine
Image: shale Image: shale
Shale is a fine-grained sedimentary rock whose original constituents were clays or muds. It is characterized by thin laminate breaking with an irregular curving fracture, often splintery and usually parallel to the often-indistinguishable bedding plane. This property is called fissility. Non-fissile rocks of similar composition but made of particles smaller than 1/16 mm are described as mudstones.
Image:  siltstone
Rocks with similar particle sizes but with less clay and therefore grittier are siltstones. Shale is the most common sedimentary rock.

65. Sandstone

Clastic, sand, round.
image: sandstone
Sandstone with iron oxide bands 
Image:  sandstone
Sandstone with quartz
Image:  sandstone with quartz
Prepared sample of sandstone
Sandstone is a sedimentary rock composed mainly of sand-size mineral or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the earth's crust. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, gray and white. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions.
Some sandstones are resistant to weathering, yet are easy to work. This makes sandstone a common building and paving material. Because of the hardness of the individual grains, uniformity of grain size and friability of its structure, sandstone is an excellent material from which to make grindstones, for sharpening blades and other implements. Non-friable sandstone can be used to make grindstones for grinding grain (e.g. gritstone).
Rock formations that are primarily sandstone usually allow percolation of water and are porous enough to store large quantities, making them valuable aquifers. Fine-grained aquifers, such as sandstones, are more apt to filter out pollutants from the surface than are rocks with cracks and crevices, such as limestones or other rocks fractured by seismic activity.

Metamorphic – Tertiary; igneous or sedimentary that is baked and/or has been placed under a great deal of pressure

71. Schist(1)

Foliated, medium-high hardnes
Image:  Schist
The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is produced. By definition, schist contains more than 50% platy and elongated minerals, often finely interleaved with quartz and feldspar.

74. Schist (2)

Foliated, medium-high hardness
Image:  schist
muscovite schist
Image: muscovite schist
Manhattan schist, from Southeastern New York
Schist - metamorphic rock containing abundant obvious micas, several millimeters across. Shale is the parent rock of schist. Several types of schist may be recognized, based on minerals which may be present:
Mica schist (muscovite schist, biotite schist)
Garnet schist
Chlorite schist
Kyanite schist
The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is produced. By definition, schist contains more than 50% platy and elongated minerals, often finely interleaved with quartz and feldspar.
The individual mineral grains in schist, drawn out into flaky scales by heat and pressure, can be seen by the naked eye. Schist is characteristically foliated, meaning the individual mineral grains split off easily into flakes or slabs. The characteristic flaky texture of schist gives rise to the adjective "schistose".
Most schists have in all probability been derived from clays and muds which have passed through a series of metamorphic processes involving the production of shales, slates and phyllites as intermediate steps. Certain schists have been derived from fine-grained igneous rocks such as basalts and tuffs. Most schists are mica schists, but graphite and chlorite schists are also common.
Schists are named for their prominent or perhaps unusual mineral constituents, such as garnet schist, tourmaline schist, glaucophane schist, etc.
The word schist is derived from the Greek meaning "to split", which is in reference to the ease with which schists can be split along the plane in which the platy minerals lie.
Schists are frequently used in building houses or walls, as many are quite durable and strong. However it should be noted that many foundation problems with buildings both large and small are due to the Schist decaying or even the failure of the mortar. This in turn lets water into the joints thus weakening the schist further.
Most of the building foundations built in the 1920s and 30s within the New York city area used schist. Decorative rock walls on houses in the area also used a schist called "Yonkers Stone" which is no longer available. This schist was particularly hard and color fairly consistent.

74. Gneiss

Foliated, High hardnes
Image:  gneiss

Gneiss - (pronounced "nice") - a banded or striped rock with alternating layers of dark and light minerals. The dark layers commonly contain biotite, and the light layers commonly contain quartz and feldspar.
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from preexisting formations that were originally either igneous or sedimentary rocks. Gneissic rocks are coarsely foliated and largely recrystallized but do not carry large quantities of micas, chlorite or other platy minerals. Gneisses that are metamorphosed igneous rocks or their equivalent are termed granite gneisses, diorite gneisses, etc. However, depending on their composition, they may also be called garnet gneiss, biotite gneiss, albite gneiss, etc. Orthogneiss designates a gneiss derived from an igneous rock, and paragneiss is one from a sedimentary rock. Gneissose is used to describe rocks with properties similar to gneiss.
The word "gneiss" is from an old Saxon mining term that seems to have meant decayed, rotten, or possibly worthless material.
Image:  gneiss

Augen gneiss

The Acasta Gneiss is the oldest known crustal rock in the world.
Image:  Augen gneiss from Rio de Janeiro, Brazil
Augen gneiss from Rio de Janeiro, Brazil
Augen gneiss is a coarse-grained gneiss, interpreted as resulting from metamorphism of granite, which contains characteristic elliptic or lenticular shear bound feldspar porphyroclasts, normally microcline, within the layering of the quartz, biotite and magnetite bands. Etymology: from the German augen, meaning "eyes".

68. Marble

Non Foliated. From conglomerate or Breccia, hcl test after scratching.
Image:  marble Image:  marble
Marble - fizzes in acid because its dominant minerals is calcite (or dolomite). The parent rock is limestone (or dolostone).
Marble is a metamorphic rock resulting from the metamorphism of limestone, composed mostly of calcite (a crystalline form of calcium carbonate, CaCO3). It is extensively used for sculpture, as a building material, and in many other applications. The word 'marble' is colloquially used to refer to many other stones that are capable of taking a high polish.

69. Quartzite

Non Foliated, from standstone or Arkose, no frizzing from HCL test.
Image:  quartzite Image: quartzite
interlocking grains of quartz. Scratches glass. The rock fractures through the grains (rather than between the grains as it does in sandstone). The parent rock is quartz sandstone.
Quartzite is a hard, metamorphic rock which was originally sandstone. Through heating and pressure usually related to tectonic compression within orogenic belts, the original quartz sand grains and quartz silica cement were fused into one. Pure quartzite is usually white to grey. Quartzites often occur in various shades of pink and red due to varying amounts of iron oxide. Other colors are due to impurities of minor amounts of other minerals.
Orthoquartzite is a very pure quartz sandstone composed of usually well rounded quartz grains cemented by silica. Orthoquartzite is often 99% SiO2 with only very minor amounts of iron oxide and trace resistant minerals such as zircon, rutile and magnetite. Although few fossils are normally present the original texture and sedimentary structures are preserved.
In true metamorphic quartzite, also called meta-quartzite, the individual quartz grains have recrystallized along with the former cementing material to form an interlocking mosaic of quartz crystals. Minor amounts of former cementing materials, iron oxide, carbonate and clay, are often recrystallized and have migrated under the pressure to form streaks and lenses within the quartzite. Virtually all original textures and structure have usually been erased by the metamorphism.

67. Slate

Foliated, low hardness, from shale
Image:  slate Image:  slate
Slate is a fine-grained, homogeneous, metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low grade regional metamorphism. The result is a foliated rock in which the foliation may not correspond to the original sedimentary layering.
Slate is mainly composed of quartz and muscovite or illite, often along with biotite, chlorite, hematite, and pyrite along with, less frequently, apatite, graphite, kaolin, magnetite, tourmaline, or zircon as well as feldspar. Occasionally, as in the purple slates of North Wales, ferrous reduction spheres form around iron nucelei, leaving a light green spotted texture - the spheres sometimes deformed by a subsequent applied stress field to ovoids, which appear as ellipses when viewed on a cleavage plane of the specimen.

75. Anthracite Coal

Non Foliated, hard.
Image: anthracite coal
Anthracite (Greek Ανθρακίτης, literally "a form of coal", from Anthrax [Άνθραξ], coal) is a hard, compact variety of mineral coal that has a high luster. It has the highest carbon count and contains the fewest impurities of all coals, despite its lower calorific content.
Anthracite coal is the highest of the metamorphic rank, in which the carbon content is between 92% and 98%. The term is applied to those varieties of coal which do not give off tarry or other hydrocarbon vapours when heated below their point of ignition. Anthracite ignites with difficulty and burns with a short, blue, and smokeless flame.
Other terms which refer to anthracite are blue coal, hard coal, stone coal (not to be confused with the German Steinkohle), blind coal (in Scotland), Kilkenny coal (in Ireland), crow coal (or craw coal from its shiny black appearance), and black diamond. The imperfect anthracite of north Devon and north Cornwall (around Bude) in England, is used as a pigment, is known as culm. Culm is also the term used in geological classification to distinguish the strata in which it is found and similar strata in the Rhenish hill countries are known as the Culm Measures. In America, culm is used as an equivalent for waste or slack in anthracite mining.

See Mineral List
About My Rocks, Crystals & Minerals

Another ramdom picture
Image: Pretty rock

None of these pictures are by me. I found them from various places on the Internet for my own use in studying for my class tests. Most of this information was extracted from
And some from and other places.
If you want to print this it is about 20 pages.


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