1) Why are silicate rocks the most common on Earth? a. The most common minerals
ID: 109181 • Letter: 1
Question
1) Why are silicate rocks the most common on Earth?
a.
The most common minerals are silicates.
b.
Iron, oxygen, silicon and magnesium make up 91.2% of the Earth’s mass.
c.
Oxygen, silicon, iron, and hydrogen make up 91.2% of the Earth’s mass.
d.
Both a and b are correct.
e.
Both a and c are correct.
2) The theory of plate tectonics ____________.
a.
incorporates continental drift but not sea-floor spreading
b.
incorporates sea-floor spreading but not continental drift
c.
incorporates and explains both sea-floor spreading and continental drift
d.
does not incorporate sea-floor spreading or continental drift
a.
The most common minerals are silicates.
b.
Iron, oxygen, silicon and magnesium make up 91.2% of the Earth’s mass.
c.
Oxygen, silicon, iron, and hydrogen make up 91.2% of the Earth’s mass.
d.
Both a and b are correct.
e.
Both a and c are correct.
2) The theory of plate tectonics ____________.
a.
incorporates continental drift but not sea-floor spreading
b.
incorporates sea-floor spreading but not continental drift
c.
incorporates and explains both sea-floor spreading and continental drift
d.
does not incorporate sea-floor spreading or continental drift
Explanation / Answer
1) The most common minerals are silicates.
Almost 85% of the atoms in the crust are oxygen or silicon atoms, and as a result the vast majority of common (rock-forming) minerals are silicates -- combinations of oxygen and silicon primarily with the other six (most common) metals listed above. Pure silica or quartz consists of only silicon and oxygen. Aluminosilicates consist of silica in which some of the silicon atoms are replaced by aluminum atoms. This replacement is not perfectly electronically balanced, and to make up for the difference in chemical reactivity (or valence) between silicon and aluminum atoms, additional atoms -- usually sodium or potassium in a one to one ratio with the replaced silicon atoms, or calcium or magnesium in a one to two ratio -- are required. Ferromagnesian silicates consist of silica in which some of the silicon atoms are replaced by iron or magnesium atoms and again, additional atoms to make up the difference in valence between silicon and iron. Continental rocks consist mostly of aluminosilicates, but quartz and ferromagnesian silicates comprise a substantial minority. Oceanic rocks consist mostly of ferromagnesian silicates, but substantial amounts of aluminosilicates and minor amounts of quartz are also usually present. The Earth's mantle consists almost entirely of ferromagnesian silicates.
2) incorporate and explains both sea-floor spreading and continental drift.
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