Diluted hydrochloric acid is used to test for carbonate minerals such as calcite. Which rock showed evidence of carbonate minerals? A. Marble B. Obsidian C. Quartz D. Gneiss

A. Marble

Explanation:

Marble is mostly a crystalline form of calcium carbonate, CaCO3. Marble is a carbonate mineral, so it should give a positive test.

B. and C. are wrong. Quartz is a crystalline form of SiO₂ and obsidian is a volcanic glass consisting mostly of SiO₂.

D. is wrong. Gneiss is a complex mixture of quartz, aluminosilicate crystals, various metal silicates, and other noncarbonate minerals.

A) Marble

Explanation:

Limestone and marble (which is metamorphosed limestone) both have significant amounts of calcite. When tested with hydrochloric acid, rocks containing calcite or other carbonate minerals will fizz and produce bubbles.