Complex sentence: Aluminum, for example, has a density of about 2.7 grams per milliliter, but, a piece of aluminum will float on top of quicksand until motion causes the sand to liquefy.
Split into simpler sentences: Aluminum, for example, has a density of about 2.7 grams per milliliter. But a piece of aluminum will float on top of quicksand until motion causes the sand to liquefy.