What mineral is this? irregularly shaped, white with nonmetallic luster, the hardness of 2.5, shows cubic cleavage and dissolves easily in water.

The material we are talking about would be serpentine.

Explanation:

This material is available in two colours green or white and it has a hardness that amounts to 2.5. This material has a luster that is nonmetallic and more of waxy in nature.  

This feature becomes Satiny when Nature of is material is Fibrous. This material is used as an insulating material against electricity as well as heat. The property of this mineral is very close to asbestos and is used when prevention from heat and electricity is required.

Halite

Explanation:

Halite is the mineral  which is called as Rock salt shows cubic cleavage

Halite forms clear transparent crystals with perfect cubic cleavage. Halite is Table salt, the salt is an array of small cubic fragments, the result of halite’s crystal structure and perfect cubic cleavage

Cubic cleavage can be produced by breaking the sample. Halite is one of the few common minerals that, when broken into small fragments, will readily dissolve in water.

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