Igneous Rock Uses Review If an igneous rock has coarse (big) crystal grains, then it is intrusive. If an igneous rock has fine (small) crystal grains, then it is extrusive. If an igneous rock is dark and heavy it is mafic (iron and magnesium). If an igneous rock is light colored and lightweight it is felsic (feldspars and silicas). Review Minerals have distinct crystal shapes due to the arrangement of their atoms. Crystals get squished together as they grow. A combination of minerals is a rock. If the rock formed from cooling magma or lava, it is an igneous rock. Igneous Rock Uses 1) Good for building/construction. Interlocking crystals make them strong and durable (resistant to weathering). Examples: building foundations and walkways. Igneous Rock Uses 2) Interlocking crystals are durable and may be valued for their beauty. Example: granite countertops/tombstones Igneous Rock Uses 3) May contain ores of valuable metals. - A vein is a thin streak of mineral-rich fluid that fills the cracks and spaces in rocks. Turquoise Vein Gold veins -A pegmatite is a vein of extremely large grained minerals. -They sometimes contain rare elements like lithium (batteries), beryllium (x-ray tubes), and tungsten (light bulbs). Kimberlites are rare, ultramafic rocks that sometimes contain diamonds. 4) Miscellaneous uses Pumice (lava rock) floats in water due to trapped gasses. Used for soap and landscaping. 4) Miscellaneous Felsic rocks (sand, quartz) make glass, plastic, computer chips, and other electonics. 4) Miscellaneous Cutting tools (sandpaper, obsidian). 4) Miscellaneous Jewelry (silicates, obsidian)