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. | 钻石近表面下的羽状裂纹就像昆虫的翅膀，由于薄膜干涉作用形成彩虹色。视域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. | 钻石由于具有紧密的晶体结构，具有极高的抵抗磨损的能力，是地球上硬度最高的矿物，但是，钻石并不是坚不可摧的，从地幔升至地表的过程中，由于金伯利岩的快速和剧烈的喷发，钻石可能产生裂隙，甚至破裂。在高能的流水中与岩石发生碰撞同样使的钻石表面产生冲积痕。在宝石贸易中，延伸至钻石内部的表面裂纹称之为“羽状纹”，通常对钻石的净度等级有负面影响。 |
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). | 钻石内部的裂隙在极少数情况下可产生迷人的光学现象。作者最近检测了一颗重量为0.39克拉的Ib/IaA型异形深棕黄-橙色钻石，其内部含有多个羽状纹，净度为I2。这一天然特征并未经材料充填以提升净度。最大的羽裂纹位于钻石台面，类似于彩虹色昆虫翅膀。 |
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，通常见于具有解理或重复的亚显微结构的宝石中。在这颗钻石中，羽状纹的彩虹色与一层厚度与可见光波长相近的空气薄膜所引起的薄膜干涉。由于钻石与空气的折射率值具有较大的差异，因此从薄膜上下两个边界反射的入射光之间存在相位差，从而产生光的干涉现象。当使用宽波长的光源观察时，相长干涉和相消干涉分别增强或减弱默写波长，从而产生彩虹状的干涉图。 |
