Sedimentary Rocks

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Clastic vs. Non-clastic

Sedimentary rocks in two major groupsClastic (detrital)Composed of fragments of silicate minerals (mostly quartz and clay)Name largely determined by the grain size (see handout)Non-clasticComposed of various minerals (usually just one)Name largely determined by the composition

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Clastic (detrital)

Coarse grained (> 2 mm)Conglomerate (rounded pieces)Breccia (angular pieces)Medium grained (

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 chertH ~ penny, no HCl reaction: mineral is dolomite, rock is limestone (dolomitic)H ~ penny, HCl reaction: mineral is calcite, rock is limestonePenny > H > fingernail, salty taste, no HCl reaction: mineral is halite, rock is Rock saltH < fingernail, no HCl reaction: mineral is gypsum, rock is Rock gypsum

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Doing the lab CaCO3?

Test with HCl (acid).Fizz means calcite present.If its all calcite rock is non-clasticBe 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)

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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?

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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 mmMedium grained (m.g.): vis. grains to 2 mmFine grained (f.g.): gritty on teethVery 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.

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Doing the lab Components

What makes up the rockGrains? (Sand, silt, pebbles, )Of what?A single mineral?Multiple components?

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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 sortingCompositionalWell = composed of only one componentPoor = mix of several different componentsSizeWell = all grains are same sizePoor = grains are all sizesCompositional and Size sorting usually go hand-in-hand

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Other features

Include:FossilsSalty tasteObvious bedding/laminationsOoids (oolites)

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Name

UseHandout chartBookWall poster

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Questions?