Geology+-+Types+of+Rocks

Our student geologists are honing their observation skills, learning how to recognise and classify key rock types while discovering a little about rock forming environments along the way...
====1. Tylah with the standard “University of Otago; Department of Geology; Rock Set” which contains seventeen numbered rock hand samples. ==== || ====2. Firstly, the students place rock hand samples into groups as they see fit. The grouping (into rock families) can be for any reason PROVIDED they ====
 * [[image:P1320086.JPG width="352" height="265"]]

write down the reasons for their decisions.
|| 3. Katrina's exercise book notes which show the numbers of the rocks that she thinks should be grouped and her reasons for making that classification. || 4. Maddy is looking carefully at the rock samples and thinking about how they might be grouped. ||
 * [[image:P1320060.JPG]]

5. Mr Beaton explaining to Maddy how coal is formed and illustrating its layering in a sedimentary sequence.
|| 6. An example of student rock-grouping; Maddy has put two limestones together; a slate with siltstone; coal with pumice; and a basalt with conglomerate (containing volcanic clasts). ||
 * [[image:P1320077.JPG width="347" height="246"]]

into sedimentary, metamorphic, and igneous classes.

 * ====**[|Sedimentary rocks]** have clasts rather than crystals; would probably show bedding; and may contain fossils.====
 * ====**[|Metamorphic rocks]** have new minerals (the definition); may have aligned crystals which make the rocks fissile (easily split); may have mineral segregation (schistosity); and may have (deformed) layers.====
 * ====**[|Igneous rocks]** have three main groups (igneous rocks may also have bedding).====
 * ====Ore or minerals samples would be treated separately from rock samples.==== || [[image:TRANSFORMED_03.GIF align="center"]]

**The three main groups of igneous rocks:**
8. Tylah correctly using a 10x loupe. to examine a piece of Oamaru limestone. It is helpful to also look at the rock in the sun because crystal structure and cleavages may be seen in the strong light.
 * ====**fine-grained (crystals**) or glassy rocks that are generally classed as volcanic (exposed to rapid cooling);====
 * ====**coarse-grained (crystals)** rocks that are generally classed as plutonic (crystals allowed to grow in heated conditions for some time) and;====
 * ====**porphyritic rocks** – these are rocks that contain crystals grown in a plutonic environment for some time but have been blown out of the volcano so that the crystals are cemented in a fine-grained matrix.==== || [[image:P1320064.JPG width="306" height="226"]]



A **loupe** is a hands lens and is used to identify small mineral crystals and structures in rocks.
|| ====10. An effervescence (bubbles of carbon dioxide) which occurs when a drop of dilute hydrochloric acid (HCl) is placed on limestone (composed mainly of calcite, a calcium carbonate). This is a useful test to separate ==== rocks with calcite from those without. ||
 * [[image:P1320070.JPG width="324" height="244" align="center"]]

11. Scraping off a little bit of the sample (with a locking blade knife) can make identifying grain size easier i.e. siltstones from mudstones.
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12. These two samples are related; pumice and obsidian. They are both made predominately of volcanic glass. The difference is the amount of vesiculation i.e. gas bubbles present.
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 * [[image:P1320084.JPG width="319" height="256"]]

This leads to changing magma/lava compositions over time.
|| 14. This picture shows a typical cross-section of a composite volcano showing a mountain built up with lava (surface volcanic material) coming from a magma (sub-surface molten rock) chamber with, in turn, magma coming from the mantle (a partial melt of rock). ||

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 14.6667px;">a pluton (as illustrated); granite and gabbro
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