12.15ct t.w. Blue Topaz, .55ct t.w. Diamond Flower Necklace, Black Agate This 12.15 ct. t.w. blue topaz and .55 ct. t.w. diamond flower necklace is a stunning combination of color and flirtatious flair! Black agate daisies flash with blue topaz buds and twinkling diamonds. This necklace is so fun to wear, and not just because of all the compliments you'll receive! 18kt yellow gold necklace. Blue Topaz birthstones are the perfect gift for December birthdays.