Study GuideGeology–Metamorphic Rock Types1. Factors That Control MetamorphismMetamorphism happens when rocks are changed by heat, pressure, water, and stress deep insidethe Earth. Even though these conditions can strongly affect a rock’s texture and minerals, oneimportant thing usually stays the same:the overall chemical composition of the rock.1.1 Rock Chemistry: The StarƟng Point MaƩersIn most cases, a metamorphic rock keeps a chemistry very similar to its original, orparent, rock.•Aquartz sandstone, which is rich in silica, will turn into a metamorphic rock that is also richin silica.•Alimestone, which is rich in calcite (calcium carbonate), can only metamorphose into acalcium-rich metamorphic rock.Because of this, a quartz sandstonecannotchange into a calcium-rich rock. Metamorphismrearranges minerals—it does not completely change the rock’s chemistry.1.2 Temperature and Pressure: Driving Mineral ChangesTemperature and pressureare two of the most important controls on metamorphism.•Different minerals form under different combinations of heat and pressure.•Each mineral is stable only within a certain range, called itsstability field.•When temperature or pressure moves outside that range, the mineral breaks down and new,morestable minerals form.Higher temperatures also:•Cause minerals that are generallyless denseto form•Speed up chemical reactions, making metamorphism happen more efficientlyPreview Mode
This document has 16 pages. Sign in to access the full document!