ROCKS ROCKS Rocks naturally occurring combinations of minerals

ROCKS

ROCKS • Rocks: naturally occurring combinations of minerals, fossils or other hard materials. • classified by the way in which they form. • 3 rock types: igneous, sedimentary and metamorphic

IGNEOUS ROCKS Igneous Rocks: former magma (molten rock), which cooled and crystallized into solid rock • Intrusive (Inside) Igneous Rocks: form as magma cools slowly beneath Earth’s surface • • • Slow cooling rate allows crystals to grow large, so they are very visible Extrusive Igneous Rocks: form as lava (former magma) cools quickly at Earth’s surface • Rapid cooling produces small crystals, not readily

Intrusive Igneous Rocks • Granite: a coarse rock formed from the cooling of magma within the Earth (intrusive) • Composed of various amounts of quartz, feldspar, muscovite, biotite, and hornblende. • Continental crust (that stuff we live on) is primarily composed of granite…know that. quartz biotite mica (*) feldspar

Extrusive Igneous Rocks • Basalt: dark, finegrained igneous rock • • • Fine grained because it formed quickly or slowly? occurs as lava, sometimes accumulating to thicknesses of 1000 s of feet and covering 1000 s of miles cools rapidly. Volcanoes which produce basaltic lavas are non-explosive Oceanic crust is composed of basalt…know this!

Basalt – Extrusive Igneous Rock Vesicular Volcanic Bomb (*) Gases released near the surface of a lava flow create bubbles or vesicles, which are “frozen” in stone. Amygdaloidal (*)

Basalt – Extrusive Igneous Rock Pahoehoe: feature which forms on the surface of a very fluid basalt flow. 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.

Basalt – Extrusive Igneous Rock The Bottom side of this pahoehoe is rough and jagged and is called Aa.

Basalt – Extrusive Igneous Rock Flow banding • Obsidian: volcanic glass • • glassy, lustrous and appearance makes it easy to distinguish from all other rocks cooled so quickly that the minerals could not crystallize. Colors vary from black to red, black & red Apache tear (mahogany), gray, green, iridescent, snowflake. Apache Tears are little nodules of obsidian Snowflake

SEDIMENTARY ROCKS • • • Sedimentary Rocks: layered or stratified rocks Sedimentary rocks form from compaction or cementation Compaction: a squeezing together of particles/sediments Cementation: particles/sediments get glued together by dissolved minerals 2 types: Clastic Sedimentary Rock and

Sedimentary Rocks • Clastic Sedimentary Rocks: composed of particles of pre-existing rocks • • • fragments show evidence of transport Examples: Shale, Sandstone Chemical Sedimentary Rocks: composed of solids which precipitated from solutions (like salt from evaporated water) or organic process (like compacted shells from marine organisms) Sandstone Shale

Sandstone and Shale – Sedimentary Rock • Sandstone: composed of cemented sand grains • • • identified by its sandy texture and gritty feel form in beaches, sand bars, deltas and dunes Shale: very common rock made of silt and clay • • Very thin with splits along the planes. gray to black, or brown to Coconino Sandstone, the result of a Permian age coastal dune field Black shale, from the Middle Cambrian sea.

COAL – Sedimentary Rock • Coal: decomposed remains of vegetation which accumulated in a wet, low oxygen environment, such as a swamp or marsh • • Coal (sub-bituminous) out of the Cretaceous Dakota Formation of north-eastern Arizona. Examples include: Peat and Lignite used as fuels

Sedimentary Rock • Features of sedimentary rock include: • Layering • ripple marks • mud cracks • salt casts

Sedimentary Rock • Features of sedimentary rocks are clues to how the rocks are formed, and help us understand the history of the Earth

Weathering, Erosion, and Deposition • Weathering: breaking down of rock through contact with the Earth's atmosphere and waters • Erosion: process by which soil and rock are removed from the Earth's surface by wind or water, and then transported and deposited in other locations Deposition: process by which sediments, soil, and rocks are added or deposited to an area Funny Video • • All rocks on Earth are locked into a system of cycling and