Aqua Obsidian also known as volcanic glass.  You may remember when Mt. St. Helens erupted we got Helenite that dark emerald green stone.  This material while could be confused with Aquamarine the price will tell you it is not.  (Aquamarine very expensive). All except A has been design on a "flip" band so called as one side flips up straight, the straight (flat) side is always worn to the center of the hand.  A has been designed on a saddle band (think English riding saddle wide and flat on top tapering to narrow).  All the rings have been accented with solid 14kt gold.

A) 1 1/4"long x 5/8"wide; B) 7/8"long x 1/2"wide; C) 1/2" x 1/2"; D) 1/2" x 1/2"; E) 3/4" x 3/4"; F) 1/2" x 1/2"