150Lec3 - Lecture #3: Rocks (Abbott, pp. 44-46, 190-200,...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Lecture #3: Rocks (Abbott, pp. 44-46, 190-200, 229-234) Underlined terms have internet links. What are Rocks? Rocks are assemblages of two or more minerals (Abbott, p. 497) or other solid substances. Some rocks mainly contain organic compounds ( coal ) or volcanic glass , which are not minerals. Rocks are divided into three major types: igneous , sedimentary , and metamorphic . Igneous rocks solidify from molten rocks. They may be divided into extrusive (erupted or volcanic) and intrusive (igneous rocks that solidify deep within the Earth). Magma refers to molten rock deep within the Earth. If the melt reaches the Earth’s surface, it’s called lava . Intrusive (also called plutonic ) rocks are generally coarser grained (that is, the minerals are larger) than volcanic (extrusive) rocks, since intrusive rocks cool more slowly deep within the Earth and their minerals have more time to grow larger. In contrast, lavas may come into contact with surface water and cool rapidly (quench) to form volcanic glass (Figure 8.19, p. 197). Cool air will also quickly solidify lava and produce a lot of glass. Because plutonic rocks are deep (kilometers) within the Earth, they are insolated from cool surface water and air, and do not contain glass. Intrusive (Plutonic) and Extrusive (Volcanic) Igneous Rocks: Sediments (like sand, gravel, and mud) form from water (including ice) and wind breaking down rocks at the Earth's surface. Sediments may accumulate in rivers, lakes, glaciers, deserts, seas, and oceans. Sediments may also consist of minerals that have precipitated from water (such as calcium carbonate, CaCO 3 , or sodium chloride, NaCl). Once sediments are buried, they may be compacted and transformed into sedimentary rocks at temperatures of about 40-200 o C and depths as great as 8 kilometers or more. Limestones , sandstones and shales are examples of sedimentary rocks. Limestones are common around Lexington and mostly consist of the mineral calcite (calcium carbonate, CaCO 3 ). They formed from the burial of ancient sea sediments. Sandstones mostly
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
consist of quartz (SiO 2 ) sand grains (Figure 10.19, p. 257). Shales mainly contain clay ("muds") and other very fine-grained minerals. Metamorphic rocks are igneous or sedimentary rocks that have been crushed, heated or otherwise severely altered in the subsurface without melting . As discussed later, metamorphic rocks may form from the grinding of rocks in faults during earthquakes. Also, deep in the subsurface, at temperatures greater than about 200 o C, sedimentary rocks generally begin to convert into metamorphic rocks. Depending upon the amount of water, wet metamorphic rocks will melt and become magmas as low as 600-750 o C. Dry metamorphic rocks may not melt until at least 900 o C. Once the melts cool, the resulting rocks are classified as igneous. Marble
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 07/14/2011 for the course GLY 150 taught by Professor Henke during the Spring '08 term at Kentucky.

Page1 / 7

150Lec3 - Lecture #3: Rocks (Abbott, pp. 44-46, 190-200,...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online