Australian Opal "triplets" are composed of three "layers". A thin slice of crystal Opal is adhered to Black Opal or Bouler Opal "Potch" (Opal without colour) with a cap of quartz covering and protecting the gem. The quartz crystal cap is extremely strong (7-8 on the Mohs scale) making triplets additionally popular due to their durability. The layers are adhered with a silica based glue that has the same "co-efficient of expansion" as the Opal and quartz layers.
This allows the Triplet to expand (in heat) and contract (in cold) at a uniform rate so that delamination does not occur over time. Australian Opal Cutters triplets are therefore waterproof and guaranteed against delamination (the process of the layers separating over time when affected by water). Triplets are also the best way to match with earrings as pairs provide a colour match that is extremely difficult to match in Solid Opal pieces simply because the "layers" are cut from the same original gem providing almost identical colour matching. Triplets are 100% guaranteed natrual and genuine Opal and provide intense genuine natural Australian Opal colours without the high prices you have to pay for a solid Opal.