GEOL 1111 Lab 8: Igneous Rocks Identification Igneous Rock Sample Identification. From the Samples to Identify listing find (sample number and name): EARTH SCIENCE LAB Igneous Rock Identification Igneous Rocks igneous rocks are ecchs which solidify from molten maderial (magma). Cooling of the magma can occur beneath the surface (plekeric) or an the surface (volcaric) igneous rocks can be idectifed by the delermination of the composition and taxture of the rock. Once these fwo charactaristics have been identied, the ignecus Rock identifcation chart is used to idensfy the rock name. Composition Compesitian of igreous rocks is properly identfied by deteemination of the rock's chemical composition. This, however, requires chemical equipment and apparatis thit is unawallable in this lab. Fortunatey determination of the exact chemical composition is not necessary Coloc is often an indieater of gray, tan and pink, indicate a felsic composicn. Feisic composicns are rich in selea (SiO2). Dark colors, such as black and dack brown, indicate a mafic or usramafic correoticion. Mafe compositons are poor in slica, but rich in iron (Fe) and magnesium (Mg). Intermodiate compesitions have an intermediate color, often gray ce consiating of equal parts of dark and light mineral, Beware that even though an igneous rock may have a felsic compoeition (Wy)t color), the rock can contain dark oolored minerals. Maffe rocks may contain light colored minerals as wel. As mertioned above, the