1) The student sampled rocks in the southern Sierra Nevada mountains in California, an area formed primarily of granite dating back to the Triassic period.
2) The first sample is identified as granite based on its coarse grain and black and white speckled pattern indicating high quartz and low feldspar content.
3) The second sample is identified as schist based on its smaller grain size and slight orange hue from iron oxide impurities.
2. Sampling Area
• My sampling area was the southern Sierra-Nevada mountain range in
California. The majority of this area is formed by granite, which began to
form as long ago as the Triassic period. When the oceanic plate began to
dive under the north American plate, plumes began to form deep
underground. These plumes helped cause extensive volcanism in the area
prior to the ice age, pushing these large deposits to the surface. However
limestone, marble and schist deposits can also be found in this area.
3. Sample 1
• I believe this sample to be granite, the
igneous rock that forms the majority
of the sampling area. The grain
appears to be very coarse and has a
black and white speckled pattern
associated with high quartz and low
feldspar content. High feldspar
content in granite usually gives it a
pinkish color.
4. Sample 2
• I believe this sample to be Schist
(metamorphic) due to its smaller grain
size (compare to the granite behind it)
and its orange hue. The slight orange
tint comes from a portion of iron
oxides in the rock.
5. Sample 3
• I believe this sample to be Marble (metamorphic). Depending on mineral
impurities Marble can be almost any color.
6. Sample 4
• I believe this to be Limestone
(sedimentary). Limestone dissolves
more easily than other rocks , as
water can pick up small amounts of
carbon dioxide forming a weak acid.
This rock was probably in a stream or
river at some point smoothing its
edges.
7. Sample 5
• I believe this sample to be Quartzite
(Metamorphic) due to its appearance
of almost 100% quartz content and
medium grain. Quartzite is formed
from sandstone or chert recrystallizing
under high pressure and temperature.
8. References
• Tarbucks, E., & Lutgens, F. (2011) Earth: An Introduction to Physical
Geology. New Jersey. Pearson Education
• http://sequoia.virtualsierra.com/seqGeology.htm
• http://geology.about.com/library/bl/blrockident_tables.htm
