7Answer Magma is molten rock inside the Earth Lava is molten rock on the surface of the Earth
8Rock Characteristics Use to tell history, origin of the rock Did it form inside or on the surface of EarthHow long did it take to form?
9Rock CharacteristicsRock Texture: Relates to size of the mineral crystals. The size of the crystal indicates the amount of time it takes to cool down and form a solid object. The larger the crystals, the longer the time of formationTypes of textures-Coarse Grained: Large crystalsFine Grained : Small crystals. Will usually not be able to see crystals without microscope
10Other texture types Glassy: No crystals, even under a microscope Indicates very rapid cooling of lava (seconds)Vesicular: Rocks with holesHoles indicate escape of gases during rapid cooling
11Color (2nd Characteristic) Color indicates composition of the rockLight colored rocks: indicate rocks with high concentrations of Si, O, K and NaWhite, pinks and grayThese rocks have a Felsic compositionFormed within continents
12Color Dark colored: Color dominated by dark greens and black These rocks have high concentrations or Fe, Mg and CaThese rocks have a mafic compositionThese rocks are formed within oceans
13Nothing is black or white… A lot of rocks are combinations of felsic and mafic materialsColor will be medium dark (usually dark gray)These have an intermediate composition
16Density (3rd Characteristic) Mafic rocks are generally more dense than Felsic rocks
17Rock NamesMatch the name to your rock sample based on your observationsBasalt- fine grained , maficGabbro- coarse grained, maficGranite- coarse grained, felsicObsidian- glassy, maficPumice- vesicular (very small holes), felsicTuff- fine grained, felsicScoria – vesicular (larger holes), mafic
18Types of volcanic rocks Obsidian: Mafic, Glass, no crystals, instant solidTuff, pumice: Felsic, Tiny crystals, with holes, quick solidificationBasalt: Mafic, tiny crystals, lava solidificationGranite, Felsic, large crystals, magma solidification without exposure to air
19What do the rocks tell about its history… Basalt, obsidian, pumice, tuff and scoria are examples of extrusive igneous rocks.These rocks were created from the material extruded from an volcanic eruptionIn general, extrusive rocks have no crystals or very small crystals: short cooling time
20Gabbro,and granite are examples of intrusive igneous rocks Formed when magma slowing cools inside the earth before exposed through erosionFormed when magma is given a chance to slowly cool over millions of years, without being exposed to the surface of the earth
21Why do intrusive rocks grow such big crystals? Because the rocks in the interior of the Earth are poor conductors of heat, it takes a long time for the hot magma to be cooled. Thus, the intrusive igneous rocks have a coarse-grained texture due to their slow cooling.