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Classifying Rocks Geologists observe: 1.Mineral composition 2.Color 3.Texture a. Grain size b. Grain shape c. Grain pattern.

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Presentation on theme: "Classifying Rocks Geologists observe: 1.Mineral composition 2.Color 3.Texture a. Grain size b. Grain shape c. Grain pattern."— Presentation transcript:

1 Classifying Rocks Geologists observe: 1.Mineral composition 2.Color 3.Texture a. Grain size b. Grain shape c. Grain pattern

2 Igneous Rocks Classified according to their origin, texture, and mineral composition. ORIGIN: Extrusive rock – igneous rock formed from lava that erupted onto Earth’s surface Intrusive rock – igneous rock formed when magma hardens beneath Earth’s surface

3 Igneous Rocks (continued)  Texture depends on the size and shape of it’s mineral crystals.  Rapidly cooling lava forms fine grained igneous rocks with small crystals (extrusive rocks)  Slowly cooling magma forms coarse grained rocks with large crystals (intrusive rocks)  Mineral composition – low silica = dark color, no quartz / high silica = light colored rocks, has quartz inside

4 Examples of Igneous Rocks Extrusive rock – igneous rock formed from lava that erupted onto earth’s surface – Basalt Intrusive rock – igneous rock formed when magma hardens beneath earth’s surface - Granite

5 Sedimentary Rocks (from sediment to rock) Sediment: small, solid pieces of material that come from rock or living things Erosion: running water, wind, or ice loosen and carry away fragments of rock Deposition: sediment settles out of the water or wind carrying it Compaction: process that presses sediments together Cementation: dissolved minerals crystallize and glue particles of sediment together

6 Types of Sedimentary Rocks Clastic Rocks: sedimentary rock that forms when rock fragments are squeezed together (Shale, Sandstone, & Conglomerate) Organic Rocks: remains of plants and animals are deposited in thick layers (Coal & Limestone) Chemical Rocks: when minerals that are dissolved in a solution crystallize (rock salt)

7 Metamorphic Rocks Formed by heat and pressure Foliated Rocks: metamorphic rocks that have their grains arranged in parallel layers or bands – Slate & Gneiss Nonfoliated Rocks: mineral grains are arranged randomly, they do not split into layers – Marble & Quartzite

8 Dating Rocks Relative age – the age compared to the ages of other rocks Absolute age – the number of years since the rock was formed Law of Superposition – the oldest rock layer is found at the bottom Unconformity: location where new rock meets older rock beneath the surface – shows a gap in the geological record

9 Radioactive Decay Radioactive Decay: the atoms of one element break down to form atoms of another element * Occur naturally in igneous rocks Half-life in a radioactive element: the time it takes for half of the radioactive elements to decay Scientists use radioactive dating to determine the absolute ages of rocks


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