黑鑽石

黑鑽石（；又稱黑金剛石或圓粒金剛石）是韌性最強的的天然金刚石之一。它是一種不純淨、密度高的多孔隙多晶粒鑽石，由金剛石、石墨及无定形碳組成，孔隙內或會有微小晶粒沉澱物或已還原的金屬包裹體填充，使其呈各種色彩。黑鑽石主要發現於中非共和國及巴西的中海拔沖積礦床。它的自然顏色是黑色或暗灰色，孔隙率比其它鑽石高。

不尋常的性質
除了另行說明外，黑鑽石的特點在這部分是由Heaney et al. (2005)的摘要指出。

黑鑽石一般都是由豌豆大小或更大的多孔微小的黑色晶體的聚合體。最獨特的是，只有中非共和國及巴西能發現黑鑽石，極小部分發現在南非共和國，但卻沒有在通常發現鑽石的慶伯利岩中發現。利用黑鑽石晶體內的铅，發現這些晶體約於3億年前形成；然而，黑鑽石卻只發現於年輕的沉积岩中。
鑽石中包含的礦物顆粒已被廣泛研究，以尋找鑽石來源的線索。一些典型的鑽石含有常見的地幔礦物包裹體，如和鎂橄欖石，但在黑金剛石中尚未觀察到此類地幔礦物。相比之下，一些碳酸鹽含有地壳特徵礦物的自生包裹體；內含物不一定確定地殼中鑽石的形成，因為雖然明顯的晶體內含物出現在黑鑽石中常見的孔隙中，但它們可能是在黑鑽石形成後引入的。發現地殼中稀有或幾乎不存在的其他礦物的夾雜物至少部分包含在金剛石中，而不僅僅是在孔隙中：在這些其他礦物中，含有硅、碳化硅及铁‑镍的成分。沒有發現獨特的高壓礦物，包括六方碳的同质异形体藍絲黛爾石，作為夾雜物出現在黑鑽石中，儘管黑鑽石有可能是由隕石撞擊而形成的。
同位素的研究揭示更多關於黑鑽石來源的線索：黑鑽石內碳的同位數慎非常低，相比一般的鑽石，黑鑽石內碳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  is found in the mines at Kimberley and is very valuable for use in diamond drilling since the Brazilian carbonado has become so scarce."cite website|auhor=Hobart M. King, PhD, GIA Graduate Gemologist|year=2022|https://geology.com/diamond/carbonado/ 

 起源假說 
黑鑽石的起源有爭議，以下列出部分建議的起源假說：
 有機碳在地球內部的高壓下直接轉換，如最常見的鑽石形成假說。這樣黑鑽石應該能於全球發現，但現時僅發現於部分地區。
 ，如隕石在地球表面衝擊引起的。但是，絕大部分衝擊引成的六晶體都是六方金剛石，與黑鑽石不同。
 自發裂變的鈾和釷輻射誘發的形成。但輻射產生的分裂能量太小，不能創造大顆粒晶體（指直徑0.5毫米以上）的金剛石。
 由於與長時間的超級閃電雷擊相關的火變質快速過程，在漫長的地質時期中，在減少的富含有機物沉積物中累積的局部形成，已知與相似海拔的碳金剛石礦床具有相似的全球分佈。
 形成于一颗在太阳系区域附近的前代巨型恒星内部，然後通过超新星爆发来到地球。
 起源于星际物质，由於小行星的撞擊落到地球，而非源于爆发的恒星内部。
研究顯示這些黑鑽石的紅外線吸收頻譜與地外來源的鑽石的吸收頻譜近似；
selected significant peaks are due to trace abundances of the elements 氮 and 氢.
The researchers concluded with the assumption that the mineral necessarily formed in an interstellar environment. In this sense, carbonado are theorized to be akin to carbon-rich cosmic dust, likely having formed in an environment near carbon stars. The diamonds were suggested to have been fragments of a body of asteroid size that subsequently fell to Earth as meteorites.
截至2008年，上述六個有關黑鑽石形成的假說都未有得到廣泛認同；此外，有關黑鑽石內碳13和碳12的比例亦與當地沉積物的比例相同。

 地外起源假說 
黑鑽石地外起源假說的支持者認為黑鑽石源於380億年前一顆超新星爆炸時噴射出來的物質。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 隕石 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 中非共和國, 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).
不過介乎兩個國家之間的喀麥隆並未有黑鑽石開採過的紀錄。

 最大已切割鑽石 
現時世上最大的已切割鑽石是一顆名為「」的黑鑽石，達到555.55克拉，擁有55個切面，目前估價為500萬英鎊（約新台幣1.88億元）。

 參見 
超硬材料








 參考資料 

 外部連結 

Photo of porous carbonado  at National Science Foundation
Photo of glossy carbonado and article on possible extraterrestrial origins  at PBS Nova
Mystery Diamonds: Geoscientists Investigate Rare Carbon Formation ScienceDaily (June 1, 2007) Story


Category:鑽石