chalk 
(chôk)
(chôk)n.
1. A soft compact calcite, CaCO3, with varying amounts of silica, quartz, feldspar, or other mineral impurities, generally gray-white or yellow-white and derived chiefly from fossil seashells.
2.
a. A piece of chalk or chalklike substance in crayon form, used for marking on a blackboard or other surface.
b. Games A small cube of chalk used in rubbing the tip of a billiard or pool cue to increase its friction with the cue ball.
3. A mark made with chalk.
4. Chiefly British A score or tally.
tr.v. chalked, chalk·ing, chalks
Phrasal Verb: 1. To mark, draw, or write with chalk: chalked my name on the blackboard.
2. To rub or cover with chalk, as the tip of a billiard cue.
3. To make pale; whiten.
4. To treat (soil, for example) with chalk.
chalk up
1. To earn or score: chalk up points.
2. To credit or ascribe: Chalk that up to experience.
[Middle English, from Old English cealk, from Latin calx, calc-, lime; see CALX.]
chalki·ness n.
chalky adj.