Basalt

 

Ocean floors are made of basalt. Basalt was melted rock that flowed as a liquid from a volcano. Basalt can be dark gray or black when it is newly formed. Older basalt is dusty with a bright red color. Devil's Tower in Wyoming is made of basalt.

 

For more information about basalt, check out the following links.

http://seis.natsci.csulb.edu/basicgeo/BASALT/BASALT.html

http://volcano.und.nodak.edu/vwdocs/volc_images/north_america/devils_tower.html