I found this huge rock crystal by the river have no idea what it is?
Your rock is probably a piece of a sedimentary concretion.  I have collected rocks that look very similar from western South Dakota.  The yellow crystals are most likely calcite.  The dark brown colored material is also probably calcite and but might be barite.  

Acid testing using HCL should confirm if the yellow and brown area are calcite.
It will probably be difficult to perform an accurate specific gravity measurement for the rock.  My experience is that concretions are commonly quite dense (denser than calcite/dolomite) due to presence of denser minerals such as ankerite, dolomite, barite, celestite, fluorite, marcasite, pyite, sphalerite, siderite, wurzite, and galena as microscopic inclusions hidden within the matrix material.

Concretions definition from wikipedia.