Rock climbing requires a lot of physical activity. Our palms get wet and climbing gets harder as we lose grip. Climbers use chalk to avoid moisture and improve grip on holds.
In the past, calcium carbonate was used for climbing, but now it's fully replaced by magnesium - MgCO3 – magnesium carbonate. Some products contain additives to increase drying and improve grip.
Magnesium is already ground and ready to use. Put it in your Chalk Bag and you're ready to climb. This type of chalk may include additional drying agents. Some brands have finer grinds.
Loose chalk is usually a bit more expensive than a block. So it's up to your personal preference which one to choose.
Sometimes climbers accidentally spill magnesium if the chalk bag overturns. To avoid losing this precious powder, you can buy a chalk ball. This is simply a sack that is made of porous mesh material and filled with powdered chalk. Throw this ball in your chalk bag and you're ready to go. The ball evenly applies magnesium on your hands.
Related: How to Choose The Best Chalk Bag.
Chalk balls are economical because they do not spill huge amounts of powder in the air. The bad thing about sacks is that it's nearly impossible to cover other parts other than fingers and palms. If you need to cover your whole hands and wrists for crack climbing or difficult routes, you'd better have powdered chalk in your chalk bag.
Liquid chalk is simply magnesium blended with alcohol. Alcohol dries very quickly and you get evenly applied magnesium. The most important advantage of liquid chalk is that it has no chalk dust and leaves the minimal amount of chalk marks.