Shop › Custom Made Boulder Opal in Brown Matrix (as it occurred in nature) Necklace. Sterling Silver Bezel with 18k Yellow Gold Aand Blue Sapphire Image 1 of 1 Custom Made Boulder Opal in Brown Matrix (as it occurred in nature) Necklace. Sterling Silver Bezel with 18k Yellow Gold Aand Blue Sapphire $450.00 sold out 18” chain included. Handmade by local artist. Sold Out Added! 18” chain included. Handmade by local artist.