Exam 2 - Igneous Rocks

Question 1

the word igneous

Answer 1

The word igneous is derived from the Latin word ignus, meaning fire or fiery

The term igneous applies to natural process relating to the formation, movement, and cooling of molten materials—magma (hot, molten material underground), and lava (molten material flowing on or near the surface)

In geology, the word igneous applies to materials that have solidified from molten rock material, it also applies to the processes associated with the movement of molten material underground or erupting or the surface

Question 2

how are igneous rocks formed?

Answer 2

Igneous rocks are classified by their unique properties and characteristics which are related to composition of their host melt and the environmental setting where they form, underground or on the surface

Question 3

volcanoes

Answer 3

Volcanoes form where molten material erupts on the surface

Regions where volcanoes occur, both modern (active or dormant) or ancient (extinct) have a unique variety of landforms. There are at least 500 active volcanoes around the world, of which about 25 are actively erupting, spewing out lava, rock, ash, and noxious gases. It is estimated that nearly 600 million people around the world live within volcanic hazard zones

Question 4

what causes rocks to melt?

Answer 4

Rocks will melt (generating magma) if heat flow increases in an area to the point that minerals reach their melting points. Other factors that cause melting include the introduction of hot volatile fluids (water and gases) into rocks under pressure, or if there is a decrease in pressure confining hot rocks (such as the release of pressure caused by a great earthquake)

Melting ranges from only partial melting of select low-temperature minerals to complete melting under higher temperature conditions. As heat flow increases, more materials will potentially melt

Question 5

intrusive igneous rocks

Answer 5

Rocks formed from magma cooling and crystallizing underground are called intrusive igneous rocks

Question 6

extrusive igneous rocks

Answer 6

Rocks formed from cooling lava on or very near the surface are called extrusive igneous rocks

When lava cools rapidly it crystallizes quickly, preventing visible crystals from forming. Extrusive rocks include lava flows and pyroclastic material such as volcanic ash, cinders, etc.

Question 7

plutonism

Answer 7

Plutonism refers magma moving, cooling, and crystallizing underground. A pluton is a body of igneous rock formed underground

Plutonic rock is a rock formed at considerable depth by crystallization of magma and/or by chemical alteration. It is usually medium- to coarse-grained with a granitic (phaneritic) texture

Question 8

volcanism

Answer 8

Volcanism is any of various processes and phenomena associated with the surface discharge of molten rock or hot water, steam, or gases. Volcanic rock is any rock formed by volcanism

A volcanic eruption occurs when molten material under pressure is expelled on the surface. Some may be discharged into the atmosphere or oceans producing a variety of rock fragments including large blocks, volcanic bombs (blobs that may have a hard crust and a partially molten interior), cinders, and ash

Question 9

phaneritic texture

Answer 9

Phaneritic texture is a term usually used to refer to igneous rock with a larger crystal grain size and texture. It means that the size of matrix grains in the rock are large enough to be distinguished with the unaided eye as opposed to aphanitic (which is too small to see with the naked eye)

Rocks with phaneritic texture are usually intrusive igneous rocks. Magma underground cools and crystallizes very slowly allowing large crystals to form

Question 10

Aphanitic texture

Answer 10

Aphanitic texture applies to dense, homogeneous rock with constituents that are so fine grained that they cannot be seen by the naked eye

Rocks with aphanitic texture are usually extrusive igneous rocks. Magma or lava at or near the surface tends to cool very quickly, preventing large crystals from forming, so the rock typically has a very fine-grained texture

Question 11

classification of igneous rocks

Answer 11

1) mineral composition,
2) crystalline sizes,
3) general color, and
4) textural characteristics.

Question 12

felsic rock

Answer 12

Felsic is a term used to describe molten material (magma), minerals, and rocks which are enriched in the elements such as silicon, oxygen, aluminum, sodium, and potassium. The term combines part of the words “FELdspar” and “SILica”. Most felsic minerals are light in color and have a density less than 3 grams per cubic centimeter (g/cm3) . Felsic minerals produce felsic rocks. Common felsic minerals include quartz, muscovite, and feldspars. Granite and rhyolite are common felsic rocks

Question 13

malfic rock

Answer 13

Mafic is an adjective describing molten material (magma), minerals, or rocks that are enriched in magnesium and iron;. The term combines part of the words “magnesium” and “ferric” (ferric iron are compounds with the Fe+3 ion). Most mafic minerals are dark in color and the relative density is greater than 3 grams per cubic centimeter (g/cm3). Common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include basalt and gabbro

Question 14

felsic rock examples

Answer 14

granite - a common, coarse-grained (crystalline), light-colored, hard plutonic (intrusive igneous) rock consisting chiefly of quartz, orthoclase or microcline (feldspars), and mica. Granite is found in plutonic rocks that have been exposed by erosion

rhyolite - a pale fine-grained volcanic (extrusive igneous) rock of granitic composition. Rhyolite is common in continental volcanic regions with notable deposits around Yellowstone and volcanic centers throughout the Great Basin region extending from Nevada to New Mexico

Question 15

intermediate rocks

Answer 15

refers to rocks that are in-between felsic and mafic in mineral composition. Intermediate rocks tend to be pale to medium gray in color and subdivided into two groups, dacitic rocks and andesitic rocks

Question 16

intermediate rocks examples

Answer 16

Granodiorite—a coarse-grained (crystalline) plutonic igneous containing quartz and plagioclase, intermediate between granite and diorite in composition. The rocks exposed in the Sierra Nevada Range (including Yosemite National Park) are mostly granodiorite

Dacite—an extrusive igneous (volcanic) rock with an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. Lassen Volcano in northern California and many volcanoes in the Cascade Range are dacitic in composition

Question 17

intrusive rock examples

Answer 17

Diorite—a crystalline intrusive igneous rock intermediate in composition between granite and gabbro, consisting essentially of plagioclase and hornblende or other mafic minerals; having a “salt and pepper”-like appearance. Diorite is found in mountain ranges throughout the Pacific Northwest

Andesite—A fine-grained, brown or grayish volcanic rock that is intermediate in composition between rhyolite and basalt, dominantly composed of plagioclase feldspar. Andesite is the most abundant rock found in the volcanic rocks of the Cascade Range extending from northern California into British Columbia

Question 18

AA and pahoehoe rock

Answer 18

Materials ejected from volcanic eruptions have some unique characteristics. Some are of interest to the gem community, not that they are gems or considered precious, but they can be cut or shaped into interesting variety of uses for jewelry and art. Visitors to Hawaii are introduced to the terms pahoehoe (pronounced “pā-hoi’hoi’) and a’a (ä’ä) (Figures 7-27 and 7-28). Pahoehoe has a ropey fluid texture formed when hot basaltic lava cools quickly. A’a is lava rock with a rough, blocky surface when a lava flow continues to move slowly as it cools, and congealed rock breaks into rough pieces

Question 19

cinder cone

Answer 19

A cinder cone is a cone-shaped hill formed around a volcanic vent by fragments of lava (blocks, cinder, ash) blown out during eruptions (Figures 7-42 and 7-43). Cinder cones and lava flows can form from a vent or series of vents associated with an eruption

Question 20

shield cone

Answer 20

A shield cone is broad, domed volcano with gently sloping sides, characteristic of the eruption of fluid, basaltic lava. The large volcanoes on Hawaii are shield cones (Figure 7-44), including Kilauea and Mauna Loa volcanoes. Shield cones are formed from very hot lavas

Question 21

composite cone

Answer 21

A composite cone (also called stratovolcano) is a typically tall and large, steep volcanic cone built up of many layers of both lava and pyroclastics (tephra, pumice, and volcanic ash), often created by a series of cyclic eruptions in which pyroclastics are created by explosive eruptions until the vent is open, then lava flows occur (Figure 7-45). Most large continental volcanic cones are this type

Question 22

dome volcano

Answer 22

A dome volcano is a volcano composed of lava domes; a lava dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Lava domes can vary from basalt to rhyolite in composition although most preserved domes tend to have high silica content

Question 23

dike

Answer 23

A dike in a vertical or near vertical wall of igneous rock formed where magma squeezed into a fault zone or fracture before cooling and crystallizing. Dike form in volcanic regions, and often appear as dark castle wall-like features on landscapes where the host rock surrounding the intrusion have eroded away

Question 24

sill

Answer 24

abular, typically more horizontal than vertical, sheet of intrusive igneous rock that has intruded between layers of older rocks. Dikes and sills can form simultaneously of at different stages in igneous activity in an area