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Layered intrusions consist of several layers of igneous rock that has intruded into the upper-reaches of the crust. The separation of the layers is due to differences in melting point that depend on the silica content of the rock. Higher silica rocks have a lower melting point and thus rise higher towards the surface. Geologica generates three layers: peridotite (ultra-mafic), gabbro (mafic) and diorite (intermediate). Many types of ore deposits are generated in layered intrusions. Peridotite contains magnesite, ferrovanadium ore, and pentlandite deposits, as well as serpentine veins. Diorite contains ilmeninte, chromite and vermiculite. Both types of deposits will extend into the intervening gabbro.