Rocks and Fossils PDF

5 - Rocks and Fossils Notes Status Done Lab Notes Status In progress Systematics L5 - Mollusca 🗿ROCKS 🪨 → Natural aggregate of minerals and/or particles, cannot be described by...

5 - Rocks and Fossils Notes Status Done Lab Notes Status In progress Systematics L5 - Mollusca 🗿ROCKS 🪨 → Natural aggregate of minerals and/or particles, cannot be described by means of chemical formulas and form bodies that are well confined in space Crystalline (igneous) - magma cooling down or hight P-T conditions Intrusive volcanic → slowly cooled down lava within the Earth’s crust, allowing large crystals growth (granite) - colors depend on lava composition Effusive volcanic → immediately cooled down lava, small crystals embedded in amorphous matrix (eg. porphyry) - colors depend on lava composition Metamorphic → “pressure cooking” of preexisting rocks (eg gneiss) - slow process via atom migration after fromer crystals structures are torn apart by high P-T Sedimentary - accumulation (sedimentation) of particles, which bond together by precipitation of natural cements → fossils are often preserved here (as “accessories”, extremely concentrated or lithogenic - in ocean) Clastic → accumulation/cementation of fragments of preexisting rocks (eg sandstones) - sedimentary cycle Mudstone (clay): fine-sized grains, invisible to naked eye Sandstone: sand-sized grains, visible to naked eye Conglomerate: gravel to pebble-sized grains, embedded in finer grained matrix Authigenic → accumulation/cementation of particles formed in situ (eg limestones, free clastic inputs - coral reefs, open ocean..) Limestone: calcite+aragonite+diff. crystals forms of calcium carbonate - extremely variable in color: WHITE when pure, 5 - Rocks and Fossils 1  GRAY/BLACK when rich in organic matter, YELLOW/RED/BROWN when rich in iron or manganese → Possible grains in limestone: skeletal fragments of marine organisms (corals, foraminifera, crinoids, calcareous algae) - BIOCLASTIC LIMESTONE - or OOLITHS (formed in shallow, highly energetic tropical waters → Can turn into “Dolostone” when exposed to particular conditions (like a magnesium replacement of limestone or of lime mud before lithification) - hazelnut/pink and spongy Mixed → mixing of autochthonous and exotic (=clastic) particles (eg marls), formed in transitional areas like offshore shelf settings 5 - Rocks and Fossils 2