Which black, igneous rock was used by the Mayans to make their sword blades?
Igneous rock of even small crystals after extrusion, the resulting rock may be mostly glass (such as the rock obsidian). If the cooling of the lava happened more slowly, the rock would be coarse-grained. Because the minerals are mostly fine-grained, it is much more difficult to distinguish between the different types of extrusive igneous rocks than between different types of intrusive igneous rocks. Generally, the mineral constituents of fine-grained extrusive igneous rocks can only be determined by examination of thin sections of the rock under a microscope, so only an approximate classification can usually be made in the field. Igneous rocks are
Igneous rock the groundmass is aphanitic, chemical classification must be used to properly identify a volcanic rock. Mineralogic contents – felsic versus mafic For intrusive, plutonic and usually phaneritic igneous rocks (where all minerals are visible at least via microscope), the mineralogy is used to classify the rock. This usually occurs on ternary diagrams, where the relative proportions of three minerals are used to classify the rock. The following table is a simple subdivision of igneous rocks according to both their composition and mode of occurrence. For a more detailed classification see QAPF diagram. Granite is an igneous intrusive rock (crystallized at