The specific gravity of a substance is the ratio of its density to the density of water. Therefore, a rock with a specific gravity greater than 1 will sink in water, while a rock with a specific gravity less than 1 will float.

Some common rocks that sink in water include:

- Granite (specific gravity = 2.65-2.75)

- Basalt (specific gravity = 2.9-3.0)

- Gabbro (specific gravity = 2.9-3.1)

- Peridotite (specific gravity = 3.2-3.4)

- Sandstone (specific gravity = 2.0-2.5)

- Limestone (specific gravity = 2.5-2.7)

Some common rocks that float in water include:

- Pumice (specific gravity = 0.9-1.2)

- Scoria (specific gravity = 1.1-1.4)

- Tuff (specific gravity = 1.4-1.8)

- Shale (specific gravity = 1.8-2.3)

- Slate (specific gravity = 2.3-2.8)

- Marble (specific gravity = 2.5-2.7)