Rocks Flashcards by Phill Phillips

THE ROCK CYCLE

Rocks are naturally occurring combinations or coherent aggregates of minerals, fossils or other hard materials. They are classified by the way in which they form. The three rock types are:
Igneous
Sedimentary
Metamorphic
All rocks on Earth are locked into a system of cycling and re-cycling known as the ROCK CYCLE.

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IGNEOUS ROCKS

IGNEOUS ROCKS are “born of fire”. In other words, they were once molten and upon cooling, the magma (molten rock) crystallized into solid rock. Igneous rocks may form deep inside the Earth or at the Earth’s surface when a volcano erupts.

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(IGNEOUS ROCKS) Intrusive or Plutonic

Slow cooling deep beneath the Earth’s surface allows crystals to grow to large size (1/8” or more). These crystals are easily visible and distinguish this group of igneous rocks as INTRUSIVE.

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(IGNEOUS ROCKS) Extrusive or Volcanic

Rapid cooling near or at the Earth’s surface, produces many small crystals that are not readily seen by the unaided eye. This group of igneous rocks is called EXTRUSIVE and are typically volcanic in origin. Cooling may be so rapid that crystals do not have a chance to form and instead a glass is produced.

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Granite-intrusive

Graphic Granite
Porphyritic
Pegmatite Mica, feldspar

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(Granite-intrusive)PEGMATITES

are classified as intrusive igneous rocks, but there is a difference. They are VERY coarse grained and strictly speaking are not crystallizing out of a magma.
The coarse grained nature is the result of crystal growth in aqueous solutions rather than in the molten liquid state.
The resulting freedom of ion motion allows the crystal to grow much larger in a shorter length of time.

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Diorite - intrusive

DIORITE is very similar to granite, but is distinguished in the hand specimen by the absence of visible quartz.

Generally it has a salt and pepper appearance (about ½ black and ½ white).

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Gabbro - intrusive

GABBRO is a coarse-grained rock that is high is iron & magnesium-bearing minerals (pyroxenes, amphiboles, plagioclase feldspar, olivene). The rocks will be dark in color, somewhat heavier than granitic rocks and devoid of quartz.

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Peridotite - intrusive

PERIDOTITE or DUNITE is composed of 90-100% olivine. As a result it is characteristically olive-greens in color.

This material is thought to have originated in the upper mantle of the Earth.

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Rhyolite – extrusive

RHYOLITE’S name comes from the Greek rhyo, from rhyax, “stream of lava”. It is formed when molten rock with the same composition as a high silica granite oozes (rhyolite is VERY viscous and does not really flow) to the Earth’s surface; and therefore cools quickly so only microscopic-sized crystals develop. The volcanoes that produce rhyolite are very explosive varieties such as Mt. St. Helens, Krakatoa and O’Leary Peak (AZ). Frequently it is banded due to flow alignment of different associated minerals (quartz, feldspar, mica, and hornblende).

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Andesite - extrusive

ANDESITE is the fine-grained equivalent of DIORITE. It tends to be a darker gray than rhyolite and is often porphyritic, with visible hornblende.

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Basalt - extrusive

BASALT occurs as thin to massive lava. flows, sometimes accumulating to thicknesses of thousands of feet and covering thousands of square miles. The volcanoes that produce basaltic lavas are relatively quiet, such as the Hawaiian Islands volcanoes. Basalt is dark, fine-grained and often vesicular and amygdaloidal.

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(Basalt extrusive) Vesicular

They have gas pockets

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(Basalt extrusive) amygdaloidal

The pockets may be filled with secondary minerals, e.g quartz, zeolites minerals, calcite, opal, etc and

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(Basalt extrusive) Pahoehoe

is a feature that forms on the surface of very fluid basalt flows. Much like the skin on a bowl of tomato soup – the surface in contact with the air begins to crystallize, while the fluid lava below continues to flow. This drags the upper, still plastic, surface into a series of smooth wrinkles.

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Obsidian extrusive

OBSIDIAN is volcanic glass (an acrystalline “solid” –actually a supercooled liquid). Its glassy, lustrous and sometimes banded appearance makes it rather easy to distinguish from all other rocks. It is composed of the elements that make quartz, feldspar and iron/ magnesium minerals that have cooled so quickly that the minerals could not develop and crystallize.
Colors vary from black to red, black & red (mahogany), gray, green, iridescent, snowflake (with the silicate mineral christobalite).
Apache Tears are little nodules of obsidian.

Perlite - extrusive

PERLITE is a light gray volcanic glass, having numerous concentric cracks which give rise to a perlitic or onion skin structure. It is generally of rhyolitic composition. It also exhibits a pearly luster.

Apache Tears are some times found embedded in perlite

Pumice - extrusive

PUMICE is highly vesicular (i.e. it has lots of gas bubble holes) and is of rhyolitic composition.
Due to the many small holes, it is lightweight and will often float in water.

Tuff - extrusive

Tuff is the accumulation of ash and small pyroclastic debris (

Volcanic Breccia - extrusive

VOLCANIC BRECCIA is pyroclastic (fire-formed fragments) and forms in explosive eruptions. It is a mix of large angular fragments and small ash.
Often, the material is hot when it comes to rest and cools (welds) into a very hard rock.

SEDIMENTARY ROCKS

SEDIMENTARY ROCKS are composed of particles derived from pre-existing rocks or by the crystallization of minerals that were held in solutions.

(SEDIMENTARYROCKS)

Fragmental or Clastic

These sedimentary rocks show evidence of transport rounding of the grains and size sorting.

(SEDIMENTARYROCKS)

Chemical/Biochemical

sedimentary rocks are the result of either precipitation of solids from solutions (like salt from water) or by organic process, like shells from marine organisms.

Breccia-Fragmental (large pieces)

Its composed of large angular pieces and clay.
The name is from the Italian word for “broken stones” or “rubble”.
Many form as the result of fault movement; others form as the result of rapid and short transportation, such as landslides.

Conglamorate-Fragmental(large pieces)

Composed of large rounded pieces and clay.CONGLOMERATES are very similar to breccias, but the fragments are rounded. The name is from the Latin conglomeratus for “heaped, rolled or pressed together”. These rocks form in alluvial fans, stream beds and pebble beaches.

Sandstone-Fragmental (small pieces)

The basic composition of this rock consist(cement) of silica, carbonates, clay, or iron.The enviorment you can find these rocks include beaches, sand bars, deltas and dunes.

Shale-Fragmental (very small pieces)

The basic composition of this rock is silt and clay particles.The color of it is usually gray to dark red, depending on the amount of oxide.You often find them in lakes, swamps , deltas and offshore marine.

Limestone-Chemical

it is composed primarily of calcite. Generally it is dense, fine-grained, and usually white to dark gray. Its most distinguishing feature is its solubility in weak hydrochloric or acetic acid accompanied by brisk effervescence. The environment of deposition if generally warm, shallow seas. Therefore, marine invertebrate fossils are common.

Limestone it is used for

- Neutralize smokestack gases. - Used as a functional filler in products such as paint, countertops & plastics. - The dust on chewing gum is ground limestone. - Mild abrasive additive to toothpaste. - Soil conditioner - Flux in processing iron and copper ores - Building and ornamental stone

Chert

CHERT is crypto-crystalline quartz. It is often the result of the dissolution of volcanic ash and is sometimes found in extensive beds, such as the novaculite of Arkansas. It has waxy luster, is translucent and fractures conchoidally. Chert can be any color, but extensive beds are generally white to gray.

GYPSUM(calcium sulfate)

is found in geographically wide-spread deposits resulting from the evaporation of a body of water, such as ocean basin or playa lake. It is soft (H=2) & usually white to gray. Three varieties are: Alabaster, Satin Spar and Selenite.

Gypsum is used for

wallboard and plasters, as an agricultural amendment and to control the set/cure time of Portland cement.

ROCK SALT - chemical

``` ROCK SALT (halite – sodium chloride) is also a deposit resulting from evaporation of a marine basin or playa lake. It has cubic cleavage and tastes salty. ```

ROCK SALT is used for

a source of chlorine and sodium, as a food supplement, in water softeners and as a road de-icer.

COAL - chemical

COAL is considered a rock, although it is not composed of minerals, but rather the decomposed remains of large volumes of vegetation that accumulated in a wet, low oxygen environment, such as a swamp or marsh.

Coal chemical is used for

Fuels for example Peat, Lignite and Sub-Bituminous & Bituminous

DIATOMITE - chemical

DIATOMITE, also known as diatomaceous earth, is composed of the siliceous shells of microscopic alga called diatoms. It is light weight and is generally white.

DIATOMITE is used for as an

abrasive, insecticide, filtering medium, and paint "flattener"

METAMORPHIC ROCKS 41s

Under the influence of heat, pressure and fluids, pre-existing rocks are modified in form and even in internal atomic structure to produce new rocks stable at the new conditions. This is done within the solid state, i.e. without melting.