Which of the following best characterizes ferromagnesian silicates?
ANSWER
They contain manganese and iron and are clear to light green.
They are mostly clear, colorless, and rich in the elements silicon and oxygen.
They contain iron and manganese, are black in color, and exhibit metallic luster.
They are black to dark-green silicate minerals that contain iron and magnesium.
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The Correct Answer and Explanation is :
The correct answer is:
They are black to dark-green silicate minerals that contain iron and magnesium.
Explanation:
Ferromagnesian silicates are a group of silicate minerals characterized by the presence of iron (Fe) and magnesium (Mg) in their chemical composition. These minerals typically have a high density and dark coloration, ranging from black to dark green. This is due to the presence of iron, which imparts the darker hues.
Examples of Ferromagnesian Silicates:
- Olivine: Green to olive-green, found in mafic and ultramafic rocks.
- Pyroxenes (e.g., augite): Black to dark green, common in basalt and gabbro.
- Amphiboles (e.g., hornblende): Black, dark green, or brownish-black, often found in metamorphic rocks.
- Biotite (a mica): Dark brown to black, commonly occurring in granites and schists.
Key Characteristics:
- Iron and Magnesium Content: These minerals are rich in iron and magnesium, which influence their physical properties such as density and color.
- Dark Colors: The high iron content results in darker colors like black, dark green, and brown.
- Silicate Structure: Ferromagnesian silicates are part of the broader silicate family, which means they contain silicon (Si) and oxygen (O) in tetrahedral arrangements.
Contrast with Non-Ferromagnesian Silicates:
Non-ferromagnesian silicates (e.g., quartz, feldspar) lack significant amounts of iron and magnesium. They are generally lighter in color (clear, white, or pale) and less dense.
Ferromagnesian silicates are abundant in Earth’s crust, especially in igneous rocks like basalt, gabbro, and peridotite. These minerals play a crucial role in geology, as they are indicators of the composition and formation processes of different types of rocks.