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Igneous Rocks Pages 129-134 Objectives – Summarize three factors that affect whether rock melts. – Describe how the cooling rate of magma and lava affects the texture of igneous rocks. • Relate cooling time to crystal size – Classify ig rx according to their composition and texture. – Describe intrusive and extrusive ig rx structures. Origin of igneous rocks • Igneous rocks are formed by _________________material from a volcano or molten material within Earth • Temps are 1600 at 60-200 km beneath the surface Why is it so hot? 1. The deep rocks are under __________________from the rocks on top 2. Also … ________________________ ______________ produce heat 3. _____________________ ______________ from formation of the planet Formation of magma Three factors affect whether rock melts 1. ______________________________________________ 2. ________________________________________________ 3. __________________________________________________ Rocks have different _________________ points based upon the ________________________composition of their minerals This means they crystallize (and melt) at different times • • • Partial Melting Different minerals have different melting points, and minerals with _____________melting points are the first to melt This creates lava with a specific composition As the magma heats up, ______________minerals melt and the magma’s composition changes Where do Igneous Rocks form? Magma—_________________ Earth Lava—___________________ Earth Cooling time=__________________ ___________________ • Magma trapped underground is insulated so it cools _______________ • As it cools, the atoms arrange themselves in patterns to form _____________ • If the magma cools slowly, the atoms have time to arrange ________ crystals. • These crystals are called ________________ _____________________ Rocks form when these mineral grains grow together. Igneous Intrusive Rocks • Rocks that form beneath Earth's surface are called _________________ ________________________ rocks. • They have crystals __________________ enough to see. • We call this texture/grain size: _________________________ Granite Granite is an ________________ _____________________ rock It cooled ____________________ inside the earth It has a ______________________________ texture Diorite—salt and ____________________ look Gabbro • A ________________, _________________, _____________________ rock from the top of Bowen's Reaction Series. Does gabbro have a high or low melting point? ________________________ Extrusive Igneous Rocks • When rocks form from molten lava _____________________ Earth's surface we call them _____________________ igneous rocks. • They cool _____________________ so the atoms don't have time to arrange themselves into patterns to form ____________________. They have a __________________-___________________ texture. • This texture is called ___________________________. Rhyolite Rhyolite is an _____________________ ______________________ rock It cooled _________________, It has small grains This is called an ___________________________ texture It has the same mineral composition as _______________________. Andesite Porphyry • This is an andesite _______________________ • A porphyry has big _______________ in a _____________________ • Matrix—fine-_________________________________ Basalt • Basalt makes up the ____________________ ______________________ • It is a ________________, _________________, _________________ rock Common Igneous rock terms Vesicular Hyaline Pegmatite Vesicular—______________________texture Scoria formed when gassy lava cooled quickly above ground. You can see where little pockets of air had been. Scoria is actually a kind of ___________ and not a mixture of minerals. Pumice • Uses – lava soap – _______________-_________________ jeans • Glass. Pumice has cooled too quickly for minerals to form. Very low density • Chemical composition, however, will be from the bottom of Bowen's Reaction series (i.e. felsic). Hyaline texture—__________________ texture • ___________________ --Volcanic glass • Notice the _____________________ fracture Pegmatite—_____________ ________________ mineral grains Rock cools extremely _____________________, so very big mineral grains form. Classification of Magmas • Mafic—high in ______________and ______________________________ • Felsic—high in _________________ and ____________________(quartz) • Mafic—_______% silica – Colors-- black, green, red • Intermediate—______% silica • Felsic—______% silica – Colors-- pink, white, light gray Composition of Igneous Rocks • _________________ —high in silica (quartz and feldspar) Light colored • _________________ —high in magnesium and iron Dark colored • ___________________ --A mixture of the two In between colored Melting point is also affected by two factors • • • • The pressure – As pressure melting point The water content – High water content=_________________melting point – Low water content=_______________________ melting point Remember a rock is made of different minerals-- Bowen’s Reaction Series When rocks melt, those with lowest melting points melt first This is called ____________________ _________________________ When rock crystallize, those with highest melting points crystallize first as the magma cools – This is called ______________________ _________________________ Igneous Rock Structures Igneous Rock formation beneath the Earth's surface • Pluton-large intrusive igneous rock body • Dike—cuts across rock layers-vertical • Sill—horizontal –parallel to existing rock layers Common Igneous Rock Pairs Type of Basaltic Andesitic Granitic lava (Mafic) (Intermediate) (Felsic) Intrusive diorite granite (phaneritic gabbro texture) Extrusive basalt andesite rhyolite (aphanitic texture)