Naturally, the purpose of @forevermarkdiamonds is to promote its gems. But the multifaceted feed is less an advertisement than a declaration of love for diamonds. Model pics, red-carpet snaps, and still-life shots all showcase the stones at their most sparkling.   (Top) A Bibhu Mohapatra model   Bridal bangles   Spring flowers   Dreamy halos   Too much? Nah.   An engaging yellow ring