Week 5 - Bowens Reaction Series Flashcards
How are igneous rocks formed?
They form from magma, either extrusive (fine-grained, volcanic) or intrusive (coarse-grained, slow cooling).
How can mineral size indicate igneous rock origin?
Large crystals indicate slow cooling (intrusive), and small crystals indicate rapid cooling (extrusive).
What is Bowen’s Reaction Series?
A ranking of silicate minerals by crystallization temperature.
What minerals are at the top of Bowen’s Reaction Series?
Olivine, Ca-plagioclase, pyroxene (high-temperature crystallization).
What minerals are at the bottom of Bowen’s Reaction Series?
Quartz, muscovite, Na-plagioclase (low-temperature crystallization).
Why don’t olivine and hornblende occur together in equilibrium?
They form under different conditions and are chemically incompatible.
Why is quartz found in many sedimentary rocks?
It is resistant to chemical and physical weathering.
How does quartz appear in thin section?
Colourless in PPL, shades of grey in XPL, no cleavage, low birefringence.
What are the two main feldspar groups?
Alkali feldspars (orthoclase-albite) and plagioclase feldspar (albite-anorthite).
How does feldspar appear in thin section?
Colourless in PPL, twinning is common, low relief, alteration to clay minerals.
What is the difference between orthoclase and plagioclase feldspar?
Orthoclase shows simple twinning, plagioclase shows polysynthetic twinning.
How does muscovite appear in thin section?
Colourless in PPL, no pleochroism, one perfect cleavage, low relief.
How does biotite appear in thin section?
Brown to yellow in PPL, strongly pleochroic, one perfect cleavage.
What are the two types of pyroxene?
Orthopyroxene (orthorhombic) and clinopyroxene (monoclinic).
How does clinopyroxene appear in thin section?
Colourless in PPL, inclined extinction, 3rd order interference colours.
How does orthopyroxene appear in thin section?
Pale green to pale brown, straight extinction, moderate to high relief.
How does tourmaline appear in thin section?
Highly variable colour, elongate prismatic crystals, colour zoning.
What are the two end members of the olivine series?
Forsterite (Mg₂SiO₄) and fayalite (Fe₂SiO₄).
How does olivine appear in thin section?
Typically anhedral to subhedral, high birefringence, alteration to serpentine and fractured.
How does garnet appear in thin section?
High relief, no cleavage, remains black in XPL.
