Black beach sand originates from broken down what?

Sand grains are formed when rock or other hard material is broken down by waves, a process that can take thousands of years. Beaches with pebbles or course sand are very young while beaches with fine sand are older. The color of sand grains comes from the original material that formed the sand.

Black sand is made of broken down fragments of volcanic rock. When a volcano erupts, lava pours out, cools down, and creates black rocks. The waves erode and break down this rock causing for black sand to be created.

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-