Sedimentary – Secondary, made from igneous rocks broken down

54. Arkose

clastic, sand, round

Arkose sandstone found in Slovakia

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

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)

Organic

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)

Another form taken by calcite is that of oolites (oolitic limestone) which can be recognized by its granular appearance.

58. 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

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.

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

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.

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.

Sandstone with iron oxide bands                       

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 hardness

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

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 hardness

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.

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.

Augen gneiss - The Acasta Gneiss is the oldest known crustal rock in the world.

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.

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.

                              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, fro shale

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.

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.

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