What Causes the Black Color Emitted from Black Smokers

Question

What causes the black color emitted from black smokers?
A) ammonia dissolution
B) steep temperature gradients
C) iron sulfide precipitation
D) elemental sulfur precipitation
E) denitrification

Accepted Answer

The black color emitted from black smokers is caused by the precipitation of iron sulfide (FeS) which is black in color. Black smokers are hydrothermal vents found at the ocean floor that emit hot, mineral-rich fluids due to geothermal activity. The fluids contain high levels of sulfur compounds which react with iron from the rocks and seawater to form iron sulfide.