layered crystals specimen what is this

[pipilo02]

This rock or mineral? specimen appears to have 2 layers and looks like its made up of crystals. This was in a rock collectors collection in Texas so I don't know where it comes from.  It's very heavy weighing exactly 2 pounds and measures about 5 inches long x 3 inches wide x 2 inches tall.  What is this?  Or is there a website that will help me id it? Just a person who likes rocks. 

[lovefindingtreasures2]

Reddit has a group called, "What is this rock?", it's very helpful.

[pipilo02]

thank you lovefindingtreasures2......just joined and posted...didn't know about it!

[jlstoner]

Looks like calcite to me.

Test with a few drops of distilled vinegar,

if you get bubbles, its likely calcite.