黑钻石

黑钻石（Carbonado；又称黑金刚石或圆粒金刚石）是韧性最强的的天然金刚石之一。它是一种不纯净、密度高的多孔隙多晶粒钻石，由金刚石、石墨及无定形碳组成，孔隙内或会有微小晶粒沉淀物或已还原的金属包裹体填充，使其呈各种色彩。黑钻石主要发现于中非共和国及巴西的中海拔冲积矿床。它的自然颜色是黑色或暗灰色，孔隙率比其它钻石高。

**不寻常的性质**
除了另行说明外，黑钻石的特点在这部分是由Heaney et al. (2005)的摘要指出Heaney。
黑钻石一般都是由豌豆大小或更大的多孔微小的黑色晶体的聚合体。最独特的是，只有中非共和国及巴西能发现黑钻石，极小部分发现在南非共和国，但却没有在通常发现钻石的庆伯利岩中发现。利用同位素分析黑钻石晶体内的铅，发现这些晶体约于3亿年前形成；然而，黑钻石却只发现于年轻的沉积岩中。
钻石中包含的矿物颗粒已被广泛研究，以寻找钻石来源的线索。一些典型的钻石含有常见的地幔矿物包裹体，如镁铝榴石和镁橄榄石，但在黑金刚石中尚未观察到此类地幔矿物。相比之下，一些碳酸盐含有地壳特征矿物的自生包裹体；内含物不一定确定地壳中钻石的形成，因为虽然明显的晶体内含物出现在黑钻石中常见的孔隙中，但它们可能是在黑钻石形成后引入的。发现地壳中稀有或几乎不存在的其他矿物的夹杂物至少部分包含在金刚石中，而不仅仅是在孔隙中：在这些其他矿物中，含有硅、碳化硅及铁‑镍的成分。没有发现独特的高压矿物，包括六方碳的同质异形体蓝丝黛尔石，作为夹杂物出现在黑钻石中，尽管黑钻石有可能是由陨石撞击而形成的。
同位素的研究揭示更多关于黑钻石来源的线索：黑钻石内碳的同位数慎非常低，相比一般的钻石，黑钻石内碳13比碳12少得很多。
Carbonado exhibits strong luminescence (光致发光 and 阴极射线发光) induced by 氮 and by 晶格空位 existing in the crystal lattice. Luminescence halos are present around radioactive inclusions, and it is suggested that the radiation damage occurred after formation of the carbonados, an observation perhaps pertinent to the radiation hypothesis listed below.

**Toughness vs. hardness**
Carbonado’s polycrystalline texture makes it more durable than a monocrystalline diamond. It is the same hardness as other types of diamond, but it is much tougher. Its polycrystalline texture allows a single abrasive granule to present multiple crystallographic orientations of the diamond crystal at the cutting surface and the hardest orientation does the most aggressive cutting.
Cutting tools made with carbonado diamond last longer and require less maintenance. Carbonado was recognized as a super abrasive in the 1800s and was more highly valued for its cutting and grinding effectiveness over other varieties of diamond. The problem with carbonado is its rarity. It is only found in two countries, and total worldwide production has only been a few tons of material. Carbonado is not an important commodity in today's abrasive market.
In the late 1800s, when De Beers was developing their diamond mines in South Africa, they preferred carbonado over their own diamonds for diamond drilling. Gardner F. Williams, General Manager of De Beers Consolidated Mines, Ltd. lamented: "Round or shot boart is found in the mines at Kimberley and is very valuable for use in diamond drilling since the Brazilian carbonado has become so scarce."

**起源假说**
黑钻石的起源有争议，以下列出部分建议的起源假说：
# 有机碳在地球内部的高压下直接转换，如最常见的钻石形成假说。这样黑钻石应该能于全球发现，但现时仅发现于部分地区。
# 冲击变质作用，如陨石在地球表面冲击引起的。但是，绝大部分冲击引成的六晶体都是六方金刚石，与黑钻石不同。
# 自发裂变的铀和钍辐射诱发的形成。但辐射产生的分裂能量太小，不能创造大颗粒晶体（指直径0.5毫米以上）的金刚石。
# 由于与长时间的超级闪电雷击相关的火变质快速过程，在漫长的地质时期中，在减少的富含有机物沉积物中累积的局部形成，已知与相似海拔的碳金刚石矿床具有相似的全球分布。
# 形成于一颗在太阳系区域附近的前代巨型恒星内部，然后通过超新星爆发来到地球。
# 起源于星际物质，由于小行星的撞击落到地球，而非源于爆发的恒星内部
截至2008年，上述六个有关黑钻石形成的假说都未有得到广泛认同；此外，有关黑钻石内碳13和碳12的比例亦与当地沉积物的比例相同。

**地外起源假说**
黑钻石地外起源假说的支持者认为黑钻石源于380亿年前一颗超新星爆炸时喷射出来的物质。After coalescing and drifting through 外层空间 for about one and a half billion years, a large mass fell to earth as a 陨石 approximately 2.3 billion years ago. It possibly fragmented during entry into the Earth's atmosphere and impacted in a region which would much later 板块构造论 into 巴西 and the 中非共和国, assumed to be the only two known locations of carbonado-diamond deposits (which is not an accurate representation of the distribution of carbonado diamondite, the poly-crystaline form).
不过介乎两个国家之间的喀麦隆并未有黑钻石开采过的纪录。

**最大已切割钻石**
现时世上最大的已切割钻石是一颗名为「The Enigma」的黑钻石，达到555.55克拉，拥有55个切面，目前估价为500万英镑（约新台币1.88亿元）。

**参见**
超硬材料
*Amsterdam Diamond 
*Bort 
*Korloff Noir 
*Material properties of diamond 
*Popigai diamonds 
*Sergio (carbonado) 
*Spirit of de Grisogono Diamond 
*Superhard material

**参考资料**

**外部连结**
 Photo of porous carbonado date=20121004062842  at National Science Foundation- Photo of glossy carbonado and article on possible extraterrestrial origins date=20220331161735  at PBS Nova- Mystery Diamonds: Geoscientists Investigate Rare Carbon Formation ScienceDaily (June 1, 2007) Story- dead-url=no