Ch. 4/5 Notes Day 1 10/26/16

Objectives Students will be able to explain the effect of temperature and cooling rate of magma on the formation of different minerals within igneous rocks

Composition of magma The type of igneous rocks that form depends on the composition of the magma. The amount of silica that is found in the magma determines the type of rock. 3 types of magma Basaltic (dark) -42%-52% silica Andesitic (medium) – 53%- 66% silica Rhyolitic (light)–more than 66% silica

Magma formation There are 4 main factors involved in magma formation: Temperature- increases with depth Pressure- increases with depth. Results in increased melting temperatures. Water content- changes the melting pt of magma. Increase water = decreased melting pt. Mineral content – In depth on the next page.

Igneous rocks from magma Igneous rocks form when molten rock, magma, cools & solidifies. This molten rock originates in the Aesthenosphere, through cracks in the lithosphere at @ 200 kilometers within the earth. The magma consists largely of elements found in silicate minerals, gasses and water vapor. Because the magma is lighter then surrounding rock it makes it's way to the surface.

The Rock Cycle

But First, What is a Rock? Rock – consolidated mineral matter So what’s a mineral? Mineral – naturally occurring, solid, inorganic elements and compounds that form crystals Where do minerals come from? The core of the earth is like a big magma soup of different elements all floating around in solution This hot magma rises and begins to cool. As it cools, the elements in the solution begin to bond and form minerals. THE TYPE OF MINERAL FORMED IS DETERMINED BY THE KIND OF ELEMENTS IN THE SOUP AND HOW FAST OR SLOW THE MAGMA COOLS

More on Minerals A mineral is any naturally occurring inorganic solid that possesses an orderly internal structure and a definite chemical composition. Properties of Minerals naturally occurring (not made by humans). inorganic (teeth, seashells, trees, etc. are excluded) solid (not a gas or a liquid) orderly internal structure definite chemical composition Examples: C Diamond NaCl Halite (Na,Ca)Al(Si,Al)Si2O8 Plagioclase

Mineral Content change In Depth Different minerals form and/or melt at different temperatures and pressures The way minerals form and melt are described by the following three processes: Fractional Crystallization Partial Melting Bowen’s Reaction Series

Partial Melting The process of some minerals melting while others remain solid as magma temperature increases. Think about chocolate chip ice cream melting. The vanilla ice cream melts, but the chocolate chips remain solid.

Fractional crystallization The process of minerals crystallizing as magma cools, and are thereby removed from the magma itself. As hot magma cools, minerals that are low in silica form first (because they form at hotter temperatures) and are no longer part of the magma “soup.” As these minerals form, the leftover magma will end up having more silica in it.

Bowen’s Reaction Series A chart that describes what minerals form at what temperatures within magma Based on partial melting and fractional crystallization Bowen discovered that minerals form in two distinct ways based on their composition Discontinuous (Left side) – minerals rich in iron and magnesium. Order (Hot to Cold)- Olivine, pyroxene, amphibole, biotite mica Continuous (Right Side)– Plagioclase Feldspar formation Order (Hot to Cold)- Calcium-rich feldspars to sodium-rich feldspars BOTH SIDES CRYSTALLIZE AT THE SAME TIME

Bowen’s Reaction Series Iron and Magnesium Rich

Crystallization Videos Fractional Crystallization https://www.youtube.com/watch?v=8gvsxTwd-Sg Crystals Forming From Solution https://www.youtube.com/watch?v=qLaEdDNHGqc Bismuth Crystals Forming https://www.youtube.com/watch?v=eHfO8pmaXMg