Geocentric Science

6 Articles About Rocks & Minerals

1

A Generalized Guide for Recognizing Igneous Rocks

There are some helpful hints to keep in mind when identifying Igneous Rocks using the New York State Earth Science Reference Tables (2010 Edition). On page 6, you will find the Scheme for Igneous Rock Identification . Texture Do you see vesicles (gas pockets)? If yes then, the rock is glassy or fine. If no, then the rock is glassy, coarse, or very coarse. Do you see many different colors or is the rock light, medium, or dark in color? If you see many different colors such as pinks

2

Facts on Igneous Rocks

Igneous rocks can form in two environments. The first environment of formation is on/close to the Earth’s surface. These rocks are called Extrusive (Volcanic) Igneous Rocks. The molten rock (lava) cools very rapidly and therefore there is not enough time to form large interlocking crystals. The second environment of formation is deep below the Earth’s surface. Rocks that form in this environment are known as Intrusive (Plutonic) Igneous Rocks. The molten rock (magma) cools very slowly formin

3

Sedimentary vs. Metamorphic Rocks. What's the difference?

Metamorphic and sedimentary rocks are very different. They form in extremely different environments. See below for some of the differences: Metamorphic Rocks Form deep below the Earth’s surface Form under extreme heat and pressure Rocks undergo re-crystallization (rocks do not melt – old bonds are broken and new bonds are created) Banding may occur (typically alternating of light and dark minerals) Metamorphic rocks are dense and typically very heavy for their size Sedimen

4

The Importance of Studying Rocks

Rocks tell the Earth’s story! By looking at a rock, one can understand the conditions that must have been present for that rock to form. For example, by looking at the sedimentary rock shale, one is able to determine the water velocity at the time (the water must have been moving extremely slowly in order for clay to be deposited and form shale). Ripple marks indicate the direction of flow, and footprints along with other fossils indicate what organisms lived during that time period in that are

5

The Rock Guide

Here’s a quick guide on how to identify a rock. Igneous Rocks Intrusive Igneous Rocks Large (visible) interlocking crystals Extrusive Igneous Rocks Porous (gas pockets) Single color (light, medium, or dark) Non-crystalline (glassy) Metamorphic Rocks Extremely dense Banding (foliated) Deformed The presence of a quartz vein, pyrite, or garnet Sedimentary Rocks Fossils Layers of sediment (visible sediment) Pieces/fragments of other rocks cemented together Please note

6

What’s the Story with Obsidian?

Obsidian is a Felsic to intermediate, extrusive igneous rock, which forms when silica-rich magma flows onto the Earth’s surface and solidifies extremely rapidly before minerals can develop and crystallize. It is classified as an amorphous solid or glass. Obsidian often appears dark green to black in color due to minerals containing magnesium and iron as well as its non-crystalline structure. Other variations of obsidian include snow-flake obsidian and rainbow obsidian.