Day 2 Pretest Flashcards
Point Counting Method
A technique in petrography that involves traversing a thin section in a grid and counting minerals at each grid point to determine modal composition.
Mode of a Rock
The proportion of minerals in a rock, expressed as a percentage of volume or weight.
Becke Line Movement
A bright line seen around a mineral grain in a liquid of different refractive index, used to determine whether the mineral has a higher or lower RI.
Idiochromatic Minerals
Minerals that exhibit color due to their inherent composition, such as Azurite (blue) and Cinnabar (red).
Allochromatic Minerals
Minerals that owe their color to trace impurities or structural defects, such as Amethyst (purple quartz with iron).
Cinnabar
The primary ore of mercury, composed of mercury sulfide (HgS), and known for its deep red color.
Metamorphic Facies
A set of metamorphic mineral assemblages that develop under specific pressure-temperature conditions, such as greenschist and granulite facies.
Troctolite
A coarse-grained, igneous rock composed primarily of olivine and plagioclase feldspar, belonging to the gabbro family.
Pleochroism
The optical property where a mineral displays different colors when viewed under polarized light from different angles.
Dichroism vs. Trichroism
Dichroism occurs in uniaxial minerals (two colors), while trichroism occurs in biaxial minerals (three colors).
TAS Diagram
A classification diagram for volcanic rocks based on total alkali (Na₂O + K₂O) and silica (SiO₂) content.
Undulose Extinction
A wavy extinction pattern observed in quartz and other minerals under a microscope, caused by strain deformation.
Desert Rose
A flower-like gypsum crystal formation that occurs in arid environments due to seasonal water fluctuations.
Solidus vs. Liquidus
Solidus is the temperature below which a substance is entirely solid, while liquidus is the temperature above which it is entirely liquid.
Tie Line in Phase Diagrams
A horizontal line connecting two coexisting phases in equilibrium within a two-phase region of a phase diagram.
Melatope
The narrowest part of an isogyre in an interference figure, representing the point where an optic axis emerges.
Isogyre vs. Isochrome
Isogyre refers to dark cross patterns in an interference figure, while isochrome refers to colored concentric rings.
Adularia
A potassium feldspar that forms in low-temperature hydrothermal veins and resembles microcline but lacks tartan twinning.
Peridotite
A coarse-grained ultramafic rock composed mostly of olivine, with varying amounts of pyroxene and hornblende.
Botryoidal Texture
A mineral habit resembling a cluster of grapes, commonly seen in hematite and malachite.
Geode
A hollow rock formation lined with mineral crystals, typically formed in volcanic or sedimentary rocks.
Monzonite
An intrusive igneous rock containing nearly equal amounts of potassium feldspar and plagioclase feldspar.
Norite
A type of gabbro rich in orthopyroxene, commonly associated with layered mafic intrusions.
Eutectic Point
The lowest temperature at which a mixture of components can melt simultaneously, forming a single liquid phase.
Peritectic Reaction
A reaction where a solid and a liquid combine to form a new solid at a specific temperature.
Miscibility Gap
A region in a phase diagram where two immiscible phases coexist instead of forming a homogeneous mixture.
Plagioclase Feldspar
A solid solution series between albite (NaAlSi₃O₈) and anorthite (CaAl₂Si₂O₈) found in igneous rocks.
Metamorphic Rock Progression
Foliated metamorphic rocks progress from slate to phyllite, schist, gneiss, and granulite with increasing metamorphism.
Udden-Wentworth Scale
A grain size classification system for sediments, ranging from clay to boulders.
Miller Indices
A system used to describe the orientation of crystal planes in a crystal lattice.
Interference Colors
Colors seen in thin sections under cross-polarized light due to variations in birefringence.
Extinction Types
Parallel extinction occurs when a mineral goes dark along cleavage planes, while inclined extinction occurs at an angle.
Crystal Forms
General forms are defined by Miller Indices {hkl}, while special forms are unique to specific crystal classes.
Twin Laws
Common twin laws include Albite twinning in plagioclase, Carlsbad twinning in orthoclase, and Japan Law in quartz.
Beryl Varieties
Beryl occurs in different colors: Emerald (green), Aquamarine (blue), Heliodor (yellow), and Morganite (pink).
Radioactive Minerals
Common uranium-bearing minerals include Autunite, Torbernite, and Uraninite.
Motif & Unit Cell
A motif is a repeating atomic arrangement, while a unit cell is the smallest repeating structure of a lattice.
Folk’s Classification of Carbonates
A classification for limestones based on allochems (grains) and matrix/cement (micrite, sparite).
Index Minerals of Metamorphism
Chlorite (low grade), Biotite, Garnet, Staurolite, and Sillimanite (high grade) indicate metamorphic conditions.
