4 Answers

Depends on what the rock is comprised from. 

Good question.  If someone tells me that I'm "dense as a rock", I really don't know how dense that is.

Maybe your teacher wants you to do some research on your own... your school textbook, Google, a reference book...

Density

Density is the term for how heavy an object is for its size. Density is usually expressed in units like grams per cubic centimeter (g/cc or g/cm3), kilograms per cubic meter, pounds per cubic inch (cubic foot or cubic yard), or pounds per gallon.

Rocks vary considerably in density, so the density of a rock is often a good identification tool and useful for distinguishing terrestrial (Earth) rocks from meteorites. Iron meteorites are very dense, 7-8 g/cm3. Most meteorites are ordinary chondrites, and ordinary chondrites have a density half as much. Most ordinary chondrites are in the range 3.0 to 3.7 g/cm3, which is denser than most terrestrial rocks. For example, limestone (2.6 g/cm3 or less), quartzite (2.7 g/cm3), and granite (2.7-2.8 g/cm3) are all common low-density rocks. Some meteorites have low densities (<3.0 g/cm3), but such meteorites are rare among meteorites. The density of basalt, one of the most common kinds of terrestrial volcanic rocks, can be as high as 3.0 g/cm3. The only types of terrestrial rocks that are more dense than meteorites are ores - oxides and sulfides of metals like iron, zinc, and lead. For example, rocks composed of hematite or magnetite (iron oxides) are often mistaken for meteorites (see concretions). Such rocks have high densities, 4.5-5g/cm3, which is greater than that of any kind of stony meteorite.