A prospector find a solid rock that is composed of quartz (density=2660 kg/m3) and gold (density=19300 kg/m3). the mass and the volume of the rock are 13 kg and 4x10^-3 m3. What is the mass of gold in the rock? What is the mass of quartz in the rock?I tried to solve and got10.55 kg gold and 1.45 kg quartz. Could you try to solve this and tell me the answers you get?
Because there's not enough silicon, and there's aluminium and I think magnesium that need to go into minerals too. So you get things like pyroxene and feldspar.
not enough Si, or too many alkali-earth-metal cations, depending on how you want to look at it. The why of that is simply that the bulk earth has that condition. Mafic rocks are what form when you melt the bulk earth composition. the bulk earth has a composition that reflects nuclear synthesis in stars.
Quartz is actually quite common in mafic igneous rocks, but as a very minor component. Whether an igneous rock contains significant quartz or not depends on the composition of the magma it crystallises from and whether that magma is undersaturated, saturated or oversaturated in silica. To form quartz the magma generally must be oversaturated in silica. Most primary mantle-derived magmas range from very slightly undersaturated to very slightly oversaturated in silica. Most mafic rocks form from such relatively unmodified mantle-derived magma, so the magma crystallise little or only minor quartz. To produce quartz-rich rocks, the magma must be modified by fractional crystallisation, contamination etc.. Such evolved magma generally lacks the Mg, Fe, Ca etc. to be able to form mafic rocks.
Of the three principal rock types (igneous, sedimentary, and metamorphic), igneous rocks can be thought of as primary rocks because they crystallize from a liquid. Sedimentary and metamorphic rocks, which we will study later, may be thought of as derivative rocks. Igneous rocks are rocks formed from the crystallization of a liquid (molten rock). Igneous rocks may be divided into two categories. Intrusive or plutonic rocks crystallize from magma beneath the earth's surface. Extrusive or volcanic rocks crystallize from lava at the earth's surface. The texture of an igneous rock (fine-grained vs coarse-grained) is dependent on the rate of cooling of the melt: slow cooling allows large crystals to form, fast cooling yields small crystals. In addition to texture, igneous rocks may are classified according to their chemical composition. The most general classification is based on the relative abundance in a rock of felsic (feldspar and silica-quartz) minerals vs mafic (magnesium and ferrum or iron) minerals.
