Kim Kardashian goes off the market :(

Kim Kardashian's engagement ring is worth almost HALF as much as her Beverly Hills mansion ... sources close to the diamond tell TMZ the rock is valued at $2 MILLION!!!!!! The ring -- designed by Lorraine Schwartz -- features a 16.5 carat emerald cut center stone flanked by two 2-carat trapezoids ... for a grand total of 20.5 carats.

We're told the stones are all "the highest clarity and color."