sedimentary rocks. clastic vs. non-clastic sedimentary rocks in two major groups clastic (detrital)...
TRANSCRIPT
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 non-
clastic 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 hand-in-hand
Other features
• Include:– Fossils– Salty taste– Obvious bedding/laminations– Ooids (oolites)– …
Name
• Use– Handout chart– Book– Wall poster
Questions?