Week 3: Earth Resources / Introduction to Rocks

This week's activities:

Resource Scavenger Hunt

Resources Scavenger Hunt brings home the connection between all the things that we use in our everyday lives and the mining that has to be done to remove the earth resources necessary to make these things.

Some links to this topic:

Introducing Rocks

Introducing Rocks is self-explanatory - be sure to read through the activity if you miss this week.

Igneous Rocks

There are two major divisions of igneous rocks:

  1. Intrusive: cool deep underground and, therefore, cool very slowly.

    The temperature at depth is not that different from the temperature of the magma itself. There is not much temperature contrast between the magma and the surrounding rock, thus it takes a very long time for intrusive rocks to cool down (ten's of thousands to hundred's of thousands of years depending on the size of the magma chamber)

    Because it takes so long to cool, there is plenty of time for the minerals to grow large (elements have time to move to the crystallization sites). Thus, minerals in intrusive rocks are big enough to see without a microscope (a coarse-grained texture). Intrusive igneous rocks include granite and gabbro.

  2. Extrusive: cool at the Earth's surface and, therefore, cool quickly

    The temperature of erupting lava varies from 1000 to about 2000°F - once it erupts it quickly cools and hardens. It may take moments to weeks for a lava flow to cool depending on its thickness. It cools so quickly because of the large temperature contrast between the lava and the air, water, or ground that it comes into contact with at the surface.

    Because it cools so quickly there isn't enough time to grow large crystals. Instead many tiny minerals grow (a fine-grained texture - there is not time for the elements to move around much, so a lot of small minerals grow). Fine-grained extrusive rocks that you will see in lab include rhyolite and basalt (those taking 8T in the Spring also will see andesite)

    If the lava cools instantly on contact with the air or water, the elements won't even have time to organize into mineral structures and volcanic glass will result (a glassy texture). Glassy extrusive rocks include obsidian and pumice. All of the holes in pumice suggest that this rock forms from gas-rich explosive eruptions where the lava rose in a frothy mass and then exploded upward throwing pumice lumps through the air.

    When lava extrudes to the surface it carries gas with it that then separates from the magma (lowered pressure at the surface allows the gas to bubble out of the magma). As the gas works its way upward out of the lava flow some of it may be trapped in the quickly hardening lava. If this happens, the gas pockets will be preserved as holes in the rock (the holes are called vesicles and the texture is vesicular). Such rocks are said to be vesicular and the rock name is modified by vesicular (example vesicular basalt)

If you miss week 3:

Read through the activities in your manual, attempt to answer the assignment, get the information for next week's quiz on the class website's Lab Schedule page, and contact me about taking the quiz that you missed (this must be done sometime before the next class). Worksheets collected for this lab will be listed on the Lab Schedule page and must be turned within a week. Click here for the syllabus information about missing class.

Quiz 2 is next week on MIneral Identification - be sure to look at the quiz info on the class website's Lab Schedule page.

Notes about the worksheets I collected:

 

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