A subsurface feather in diamond resembling an insect wing, with visible iridescence caused by thin-film interference. Photomicrograph by Matthew Hardman; field of view 2.90 mm.

鉆石近表面下的羽狀裂紋就像昆蟲的翅膀，由于薄膜干涉作用形成彩虹色。視域2.90mm。

Diamond is very resistant to scratching and is often referred to as the hardest mineral on Earth due to its compact crystal structure. However, diamond is not indestructible, and it can be fractured or even broken apart during ascent from the mantle to the earth’s surface through fast, violent kimberlite eruption. Collision with rocks in high-energy rivers also results in percussion marks on the surface of alluvial diamonds (e.g., J.W. Harris et al., “Morphology of monocrystalline diamond and its inclusions,” Reviews in Mineralogy and Geochemistry, Vol. 88, No. 1, 2022, pp. 119–166). Surface cracks extending into the interior of a diamond are referred to as “feathers” in the gem trade, and these often have a negative effect on the clarity grade.        

鉆石由于具有緊密的晶體結構，具有極高的抵抗磨損的能力，是地球上硬度最高的礦物，但是，鉆石并不是堅不可摧的，從地幔升至地表的過程中，由于金伯利巖的快速和劇烈的噴發(fā)，鉆石可能產生裂隙，甚至破裂。在高能的流水中與巖石發(fā)生碰撞同樣使的鉆石表面產生沖積痕。在寶石貿易中，延伸至鉆石內部的表面裂紋稱之為“羽狀紋”，通常對鉆石的凈度等級有負面影響。

Fractures within diamond can cause fascinating optical phenomena on rare occasion. The authors recently examined a 0.39 ct Fancy Deep brownish yellowish orange type Ib/IaA diamond containing multiple feathers and graded as I2 clarity. These natural features had not been filled with a clarity-enhancing material. The largest feather located on the table facet of the diamond resembled an iridescent insect wing (see above).        

鉆石內部的裂隙在極少數情況下可產生迷人的光學現(xiàn)象。作者最近檢測了一顆重量為0.39克拉的Ib/IaA型異形深棕黃-橙色鉆石，其內部含有多個羽狀紋，凈度為I2。這一天然特征并未經材料充填以提升凈度。最大的羽裂紋位于鉆石臺面，類似于彩虹色昆蟲翅膀。

Iridescence is an optical phenomenon caused by interference of light, typically seen in gemstones with cleavage or repeating submicroscopic structures (e.g., X. Lin and P.J. Heaney, “Causes of iridescence in natural quartz,” Spring 2017 G&G, pp. 68–81). In this diamond, the feather’s iridescence was due to thin-film interference caused by a thin film of air with a thickness similar to the wavelength range of visible light. As diamond and air have very different refractive indices, there is a phase difference between the incident light reflected from the upper and lower boundaries of the thin film, resulting in constructive and destructive interference. When viewed using a broadband light source (light consisting of a wide range of wavelengths), constructive or destructive interference intensifies or attenuates certain wavelengths (colors), respectively, producing a rainbow-like interference pattern.        

彩虹色由光的干涉作用引起，通常見于具有解理或重復的亞顯微結構的寶石中。在這顆鉆石中，羽狀紋的彩虹色與一層厚度與可見光波長相近的空氣薄膜所引起的薄膜干涉。由于鉆石與空氣的折射率值具有較大的差異，因此從薄膜上下兩個邊界反射的入射光之間存在相位差，從而產生光的干涉現(xiàn)象。當使用寬波長的光源觀察時，相長干涉和相消干涉分別增強或減弱默寫波長，從而產生彩虹狀的干涉圖。