102 GEOL quiz 2 study guide
Please know the properties or attributes are used to define a mineral.
Cleavage (lol): cleavage planes: are planes of weakness in a mineral structure. If force is applied to a
mineral, it will break along a cleavage plane and hardness (lol): hardness refers to the capacity of a mineral
to resist abrasion
Know what the 2 most abundant elements in the Earths crust are.
Silica and oxygen
What conditions of temperature and pressure do blueschist facies indicate?
High pressure, low temperature
It is at a subduction zone
Where do blueschist facies rocks form?
High pressure, low temperature
What is an index mineral?
determine the degree of metamorphism a rock has experienced. Depending on the original composition of
and the pressure and temperature experienced by the protolith (parent rock), chemical reactions between
minerals in the solid state produce new minerals. When an index mineral is found in a metamorphosed
rock, it indicates the minimum pressure and temperature the protolith must have achieved in order
for that mineral to form. The higher the pressure and temperature in which the rock formed, the higher
the grade of the rock.
Know the type of cleavage (if any) of quartz, mica, amphibole, and halite.
Quartz- has a very symmetrical structure consisting of relatively strong bonds, so it has no cleavage.
Mica-Perfect cleavage in one direction (sheet silicate)
Amphibole- amphibole group: good cleavage in 2 directions ar ~120 and ~60 degrees to each other
Halite- perfect cleavage in 3 directions at 90 degrees because of its highly symmetrical structure and
consists of relatively weak bonds.
Know what determines the hardness of a mineral.
Capacity of a mineral to resist abrasion
atoms of minerals that form at pressure high will be more close together than atoms of minerals formed at
low pressure
graphite vs. diamonds
Know the melting points, relative to each other, of the minerals that constitute the discontinuous branch of
Bowens reaction series.
Olivine, pyroxene, amphibole, biotite
SILICIC--Rhyolite, Andesite, Basalt, Komatiite--MAFIC (fine)
SILICIC--Granite, Diorite, Gabbro, Peridotite --MAFIC(course)
o Mafic melts last, silicic melts first
Know the order of crystallization of minerals in Bowens reaction series.
Olivine, pyroxene, amphibole, biotite
Rhyolite, Andesite, Basalt, Komatiite (fine)
Granite, Diorite, Gabbro, Peridotite (course)
Mafic (first to crystallize/last to melt) to silicic (last to crystallize/first to melt)
Know what causes partial melting at subduction zones
Partial melting at subduction zones: when oceanic lithosphere is forced into the mantle, melting occurs:
Dewatering of the downgoing slab. Water is released from the subducted plate and goes into the mantle
wedge/asthenosphere. Water lowers the melting temperature of rocks. This causes partial melting of the
mantle wedge. The end result is that mafic magma is produced from ultramafic rock (peridotite).
Basalt ponding at the base of the crust causes partial melting of the lower crust, which produces silicic
magma. In some cases, the silicic magma may rise all the way to the surface, and result in silicic
volcanism and batholiths.
In other cases, basalt rises in fractures and mixes with silicic composition magma generated by basalt
ponding and rising through the crust to produce intermediate composition magma. In still other cases,
basalt melts and assimilates silicic rocks as it rises throughout the Earths crust and intermediate
composition magma is produced.