Igneous Rocks Quiz

Which factor primarily controls the mineral composition of an igneous rock?

• Rock density

• Chemical composition

• Cooling rate

• Pressure changes

Why are mineralogical and textural classifications considered more practical than chemical classification?

• They are based on fossil content

• They can be used easily without chemical analysis

• They require laboratory equipment

• They are based on the rock's weight

Which mineral group in igneous rocks is silica-rich and light in color?

• Mafic minerals

• Felsic minerals

• Ultramafic minerals

• Pyroxene minerals

Which of the following is a characteristic of ultrabasic rocks?

• Very dark in color and composed mostly of mafic minerals

• High quartz content

• Light-colored due to the presence of orthoclase

• Contains mostly sodium-rich plagioclase

Acid igneous rocks usually contain what percentage of quartz?

• Less than 10%

• 10-20%

• More than 20%

• 0%

Which of the following statements about feldspar composition in igneous rocks is correct?

• Acid igneous rocks contain calcium-rich plagioclase

• Basic igneous rocks contain calcic plagioclase

• Intermediate igneous rocks contain orthoclase

• Ultramafic rocks are rich in feldspar

Which of the following statements is true about silica percentage in igneous rocks?

• Acid igneous rocks contain more than 66% silica

• Basic igneous rocks contain more than 66% silica

• Intermediate igneous rocks contain less than 45% silica

• Ultramafic rocks contain between 52-66% silica

Which type of igneous rock contains NO quartz?

• Acid igneous rocks

• Ultrabasic igneous rocks

• Intermediate igneous rocks

• Basic igneous rocks

What is the silica percentage range for intermediate igneous rocks?

• Over 66%

• 52 - 66%

• 45 - 52%

• Under 45%

Why is mineral composition commonly used for classifying igneous rocks rather than chemical composition?

• It is faster and easier to identify

• It is more accurate than chemical analysis

• It requires laboratory equipment

• It is based on fossil evidence