Pumice has a mild abrasive quality and is used in personal care and cleaning products.
Lava rocks, also known as volcanic rocks, are one of two types of igneous rocks. Igneous rocks include all rocks created by the cooling of magma. The rocks that form beneath the earth's crust, such as granite, are "plutonic rocks." Rocks formed from the cooling of lava above the earth's surface are "volcanic rocks."
Types of Volcanic Rocks
There are four primary types of volcanic rocks: andesite, basalt, dacite and rhyolite. The main difference between these rocks is the percentage of silica in their composition. From these four types, other volcanic rocks, such as obsidian and pumice, are created during the process of volcanic eruption. Depending on the speed and force of the eruption, volcanic rocks can be light and porous or heavy and dense. The faster the lava cools, the less time it has to form minerals and the lighter it will be.
Sources
While volcanic rocks can sometimes be found in a local park or natural area, for the purpose of experimenting it is best to purchase them. This ensures that the rocks are properly identified and also provides for a variety of rocks to be tested. Most cities have at least one store specializing in rock-hounding; often such stores have collections of rocks suitable for setting up experiments. Online websites, such as Science Kit and Rock Detective, also offer educational rock collections.
Experiment: Can Rocks Float?
For this experiment, you will need a collection of small rocks, including pumice, and a large plastic bowl filled 3/4 of the way with water. Drop each stone into the water, one at a time, and note whether it sinks or floats. Pumice is created by the hardening of frothy lava and is full of tiny air pockets. It also forms quickly, before minerals have a chance to form. Because of these two factors, pumice will float for an extended amount of time before eventually sinking.
Experiment: Erosion and Volcanic rocks
You will need two plastic gallon jugs with lids, water and an assortment of both igneous rocks and sedimentary rocks. Examples of sedimentary rocks, which are formed from the layering of materials rather than from lava, are sandstone, shale and natural coal. Place a layer of igneous rocks in one jug and a layer of sedimentary rocks in another. Fill the jugs a little less than 2/3 of the way with water, leaving 1/3 of the jugs empty. Holding on the lid securely, shake each jug vigorously for three minutes, mimicking the affect of water on the erosion of rocks in nature. Observe how the different types of rocks responded differently to this erosive action. What does this tell you about the composition of the rocks?
Tags: volcanic rocks, igneous rocks, sedimentary rocks, formed from, volcanic rocks
