A fantastic crystal of diamond showing twinning, this specimen is a significant thumbnail example of any mineral - particularly in that it is a diamond and most diamond crystals are either ugly, or singles, or both. Additionally, most diamond crystals, singles or not, are simply too small to be a large and impactful, competitive level of thumbnail specimen. This, however, ticks all the boxes for impactful large thumbnail crystals of a gem species. It is a floater, complete all around, and undamaged. What really elevates this piece though is that it is essentially a matrix specimen featuring a triangular-shaped, spinel-twinned diamond crystal (referred to as a macle twin) with incredible adamantine luster, sitting on top of another crystal. The lower crystal seems to be a somewhat flattened cuboctahedron, and it acts as a natural pedestal to display this "diamond triangle" straight up in the air! While we have seen and handled amazing diamond crystals including several larger, and even in the 6 figures as specimens, those have all been singles. What really sets this apart as a display specimen for those who compete or care about such things is that you have a macle twin displayed upright, and it makes for a full sized thumbnail that has the same aesthetic and size as other important thumbnail gem crystal species. The display value of this, in a case or an exhibit, is worth extra points for style and rarity both. Also, it is large — at 23.7 carats. The twin stands 1.7 cm tall. We obtained this from the private collection of a New York City multigenerational family diamond dealer who is a sightholder in the diamond dispersal. A sightholder is a company on the De Beers Global Sightholder Sales (DBGSS) list of authorized bulk purchasers of rough diamonds (per Google). Rarely, they obtain crystals in tier allotments, and even these are usually cut, or polished into fancy shaped art jewels. Recognizing the value of this specimen, he kept it and brought to my attention (a few years ago, in 2019).