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."

I'm sure it must be lovely, judging from the string of chocolate Samoas around Kim's neck.