Transcript Sedimentary Rocks

Sedimentary Rocks
Clastic vs. Non-clastic
• Sedimentary rocks in two major groups
• Clastic (detrital)
– Composed of fragments of silicate minerals (mostly
quartz and clay)
– Name largely determined by the grain size (see
handout)
• Non-clastic
– Composed of various minerals (usually just one)
– Name largely determined by the composition
Clastic (detrital)
• Coarse grained (> 2 mm)
– Conglomerate (rounded pieces)
– Breccia (angular pieces)
• Medium grained (<2 mm but still visible)
– Quartz sandstone (mostly quartz)
– Arkose (abundant feldspar – often pink)
– Greywacke (much clay – often dark in colour)
• Fine grained rocks (cannot see ind. grains)
– All “mudrocks”
– Siltstone (gritty), shale (splits easily), claystone
(smooth, slippery feel)
Non-clastic
• All one mineral (usually)
• Often “crystalline” (visibly so or VERY smooth
(with conchoidal fracture)
• Named according to mineral present (use hardness
and reactivity to HCl)
– H > glass, no HCl reaction: mineral is chalcedony, rock
is chert
– H ~ penny, no HCl reaction: mineral is dolomite, rock
is limestone (dolomitic)
– H ~ penny, HCl reaction: mineral is calcite, rock is
limestone
– Penny > H > fingernail, salty taste, no HCl reaction:
mineral is halite, rock is Rock salt
– H < fingernail, no HCl reaction: mineral is gypsum,
rock is Rock gypsum
Doing the lab – CaCO3?
• Test with HCl (acid).
• Fizz means calcite present.
– If it’s all calcite – rock is non-clastic
• Be careful to note if the rock is dominantly
calcite or just partly (i.e., is the rock all
calcite, a limestone, or just random parts,
e.g., a calcite cemented sandstone)
Doing the lab – C or NC
• C: is the rock clastic; i.e., composed of
discrete particles (grains) of silicate material
(quartz, feldspar, clays, etc.)?
• NC: is the rock non-clastic; i.e., all one
mineral, probably a non-silicate, and
probably crystalline?
Doing the lab – Grain size
• Only applicable to clastic rocks (i.e. with nonclastic rocks say “not applicable” or “n.a.”)
• Coarse grained (c.g.): > 2 mm
• Medium grained (m.g.): vis. grains to 2 mm
• Fine grained (f.g.): gritty on teeth
• Very fine grained (v.f.g.): slippery to feel
(probably with an earthy smell)
• HINT: The higher the clay content of clastic rock
the darker the colour.
Doing the lab – Components
• What makes up the rock
– Grains? (Sand, silt, pebbles, …)
– Of what?
• A single mineral?
• Multiple components?
•…
Sorting
• Only applicable to clastic rocks (for non-clastic
rocks say “n.a.”)
• Fine-grained (and v.f.g.) rocks are too fine to see
the sorting. Say “too fine to see” or “n.d.”
• Two kinds of sorting
– Compositional
• Well = composed of only one component
• Poor = mix of several different components
– Size
• Well = all grains are same size
• Poor = grains are all sizes
• Compositional and Size sorting usually go handin-hand
Other features
• Include:
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Fossils
Salty taste
Obvious bedding/laminations
Ooids (oolites)
…
Name
• Use
– Handout chart
– Book
– Wall poster
Questions?