Presentation on theme: "Rocks Are made up of minerals Ex: Granite ----- > 4 minerals Essential Minerals: always occur in the rock Accessory minerals: sometimes occur."— Presentation transcript:
Rocks Are made up of minerals Ex: Granite > 4 minerals Essential Minerals: always occur in the rock Accessory minerals: sometimes occur
Classify Rocks By How they Form! Igneous- Molten Rock cools and hardens Sedimentary – Made from sediments Metamorphic – Rocks Changed by heat and pressure
High Silica content forms light-colored rocks (FELSIC).
While lower (but only by about 25%) Silica content forms darker-colored rocks (MAFIC).
THE ROCK CYCLE Rocks are naturally occurring combinations or coherent aggregates of minerals, fossils or other hard materials. They are classified by the way in which they form. The three rock types are: igneous, sedimentary and metamorphic. All rocks on Earth are locked into a system of cycling and re-cycling known as the ROCK CYCLE. (*)
IGNEOUS ROCKS (*) IGNEOUS ROCKS are “born of fire”. In other words, they were once molten and upon cooling, the magma (molten rock) crystallized into solid rock. Igneous rocks may form deep inside the Earth or at the Earth’s surface when a volcano erupts. (*)
IGNEOUS ROCKS : intrusive Slow cooling deep beneath the Earth’s surface allows crystals to grow to large size. These crystals are easily visible and distinguish this group of igneous rocks as INTRUSIVE. Large Crystals Both large and small crystals = porphyry (some grow before others begin Texture size or arrangement of crystals To get Large: Cools below Earth’s surface
Igneous - Intrusive GRANITE is a coarse to medium-grained rock that forms from the cooling of magma deep within the Earth light color - felsic DIORITE is very similar to granite, but is distinguished in the hand specimen by the absence of visible quartz. Generally it has a salt and pepper appearance (about ½ black and ½ white).
Igneous Rocks Rapid cooling near or at the Earth’s surface, produces many small crystals. This group of igneous rocks is called EXTRUSIVE Eruption at surface Numerous holes at the surface Small mineral crystals ex: basalt No mineral crystals No mineral crystals ex: obsidian Top Part of Lava- gases trapped inside of hardened lava = scoria From lava thrown out ex: pumice ex: pumice
Igneous - Extrusive Rhyolite is a fine grained, felsic rock that forms from the cooling of lava above Earth’s surface Basalt a dark fine grained rock formed from thin to massive lava flows (mafic) Pahoehoe is a type of basalt that forms on the surface of very fluid lava flows
Igneous Review Lava Extrusive Through Volcanoes Through hydrothermal vents Magma Intrusive/Plutonic - Cools and Crystalizes in Magma Chamber
SEDIMENTARY ROCKS SEDIMENTARY ROCKS are composed of particles derived from pre-existing rocks or by the crystallization of minerals that were held in solutions Weathering : Rocks are broken into pieces by water, wind or ice Water – enter cracks, expands and breaks rocks down Rain – acid rain dissolves minerals Movement in Rivers – Collect on the bottom
Formation – Build very slowly layers will grow until environment changes Cementation – minerals acting as cement holding sediments together Compaction – pieces compact due to weight squeezing them together Precipitation – water evaporates and minerals are left behind
Unusual Formation Chemical Rocks – made up of chemical sediments or once living things Organic Rocks – made up of remains of living things
Sedimentary Features Layers Only type of rock that contains Fossils! Ripple Marks – Air or water sand, silt, and clay Concretion – water comes into contact with fossils and mineral deposits Geode – hollow rocks with mineral crystals inside
Classifying Clastic Rocks (pieces of other rocks): Conglomerate & Breccias: Large sediments Sandstones: Small grains Siltstone : Very Small grains Shale : Very Small grains Clay pressed together
Classifying Non-Clastic Rocks (minerals in water or past life): - Look at composition: calcite, halite, gypsum or quartz Limestone - Calcite and seashells Rocks Salt - Halite Rock Gypsum - Gypsum Chert (flint) - Quartz Coal – Past life
METAMORPHIC ROCKS METAMORPHIC ROCKS have changed ( meta ) their form ( morphic ). Under the influence of heat, pressure and fluids, pre-existing rocks are modified in form Original rock is called the parent rock This is done within the solid state, i.e. without melting. 3 Types of Changes that occur include: - Change in Chemistry of Rock - Englargement of crystals - Rearrangement of mineral grains
Classify Burial Metamorphism – weight of overlying rock, causes a reorientation of mineral grains Regional Metamorphism – As mountains rise, large amount of magma is forced toward the surface, it hardens into the mountain core Contact Metamorphism – Small amount of magma intrudes overlying rock The nearby Rock is altered by heat, solutions, and gases from the magma *Metamorphism is the MOST intense near the core where heat and pressure cause the formation of new minerals of existing mineral grains
Features Metamorphic rocks that exhibit parallel alignments of minerals are called FOLIATED. In these rocks, the minerals all line up perpendicular to the exerted pressure. Metamorphic rocks composed of minerals that are not elongated or flat, do not exhibit parallel alignments and are called NON- FOLIATED.
The Rock Cycle Thinking about relationships among the major rock groups
23 Major Rock Groups Igneous –Formed from a melt (molten rock) –Plutonic (intrusive):slow cooling and crystallization –Volcanic (extrusion): quick cooling at the surface Sedimentary –Formed at the Earth’s surface –Clastic (Mineral Fragments or grains, clays) –Chemical (crystalline chemical/biochemical precipitates) Metamorphic –Changed by pressure, temperature and fluids.
Fig. 2.9 MAGMA
25 Crystallization IGNEOUS
26 MAGMA IGNEOUS Plutonic Crystallization
27 MAGMA Volcanic IGNEOUS Plutonic Crystallization
28 MAGMA Volcanic IGNEOUS Plutonic Uplift Crystallization Weathering
The rock cycle demonstrates the relationships among the three major rock groups It is powered by the interior heat of the Earth As well as earth’s momentum and… The energy from the sun It involves processes on the Earth’s surface as well as the Earth’s interior It connects the “hydrologic cycle” with the “tectonic cycle”. In Conclusion…
37 MAGMA Volcanic IGNEOUS Plutonic SEDIMENT SEDIMENTARY METAMORPHIC Uplift Burial Increased P&T Melting Crystallization Weathering Erosion Transport Deposition