rough surface on the broken crystal. Quartz fractures are described as conchoidal when the fractured surface exhibits a swirl pattern on the stoneChemical composition -Calcite is a calcium carbonate mineral while quartz is a silicon dioxide crystal. Visually, you cannot tell the difference in the mineral composition, but you can perform a test to determine if the crystal you have is calcite. oCalcium carbonate reacts with an acid to produce bubbles on the surface of the crystal. To test your sample, drop dilute hydrochloric acid, lemon juice or vinegar onto the sample and watch for bubbles. Quartz does not react to a dilute acid.Igneous intrusive structures (dykes, sills, plugs, necks, etc.) and Mt. RoyalIntrusive settings -Magma invades preexisting wall rock byopercolating upward between grainsoforcing open cracks-The wall rock—magma-intrusive contact reveals high heat.oBaked zone—rim of heat-altered wall rockoChill margin—rim of quenched magma at contact-Magma invades colder wall rock, initiatingothermal (heat) metamorphism and melting. oinflation of fractures, wedging wall rock apart.odetachment of large wall rock blocks (stopping), andoincorporation of wall rock fragments (xenoliths).-Magma that doesn’t reach the surface freezes slowly.Tabular intrusions (geologists categorize intrusions by shape)
- Tend to have uniform thickness - Often can be traced laterally - Have two major subdivisions o Sill – injected parallels to rock layering o Dike – cuts across rock layering - Dikes and sills modify invaded country rock o They cause the rock to expand and inflate o They thermally alter the country rock - Dikes o Cut across pre-existing layering o Spread rocks sideways o Dominate in extensional settings Sills - are injected parallel to preexisting layering. - are usually intruded close to the surface. - Both dikes and sills exhibit wide variability in: o size. o thickness (or width). o lateral continuity. Laccoliths - A laccolith resembles a sill but formed between sedimentary layers from a more viscous magma that created a lens shaped mass that arched the overlying strata upward. Volcanic necks
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- Fall '09
- Plate Tectonics