question: Why is Carbon black but pure diamonds turn out clear?
comment: Each carbon in diamond is chemically bonded to four other carbon atoms. This produces a repeating crystal structure and changes the way the individual bonds interact (or here, fail to interact) with light. Other carbon-rich materials are either not 100% carbon like coal or tar, are disorderly like carbon black, and/or use a different bonding structure like graphite. Those materials interact strongly with light and absorb most of it. Also keep in mind that only super pure diamonds are clear. Slightly impure ones are colored (often yellow) and poor quality diamonds are practically black too. Those diamonds get used in cutting/grinding tools and drills instead of jewelry.
passages: An isotopical pure diamond is a type of diamond that is composed entirely of one isotope of carbon. Isotopically pure diamonds have been manufactured from either the more common carbon isotope with mass number 12 (abbreviated as C) or the less common C isotope. Compared to natural diamonds that are composed of a mixture of C and C isotopes, isotopically pure diamonds possess improved characteristics such as increased thermal conductivity. Thermal conductivity of diamonds is at a minimum when C and C are in a ratio of 1:1 and reaches a maximum when the composition is 100% C or 100% C.
   Section::::Optical properties.:Optical absorption.
  
  Cape series (Ia) diamonds have a visible absorption spectrum (as seen through a direct-vision spectroscope) consisting of a fine line in the violet at 415.5 nm; however, this line is often invisible until the diamond has been cooled to very low temperatures. Associated with this are weaker lines at 478 nm, 465 nm, 452 nm, 435 nm, and 423 nm.
   Section::::Production.
   Section::::Applications.:Diamonds.
  
  The diamond industry falls into two categories: one dealing with gem-grade diamonds and the other, with industrial-grade diamonds. While a large trade in both types of diamonds exists, the two markets act in dramatically different ways.
  
  Unlike precious metals such as gold or platinum, gem diamonds do not trade as a commodity: there is a substantial mark-up in the sale of diamonds, and there is not a very active market for resale of diamonds.
   Section::::Manufacture.
  
  The isotopes of carbon can be separated in the form of carbon dioxide gas by cascaded chemical exchange reactions with amine carbamate. Such CO can be converted to methane and from there to isotopically pure synthetic diamonds. Isotopically enriched diamonds have been synthesized by application of chemical vapor deposition followed by high pressure.
  
  Section::::Types.
  
  Section::::Types.:Carbon 12.
   Most "colorless" diamonds are actually tinted yellow or brown to some degree, whereas some artificial simulants are completely colorless—the equivalent of a perfect "D" in diamond color terminology. This "too good to be true" factor is important to consider; colored diamond simulants meant to imitate fancy diamonds are more difficult to spot in this regard, but the simulants' colors rarely approximate. In most diamonds (even colorless ones) a characteristic absorption spectrum can be seen (by a direct-vision spectroscope), consisting of a fine line at 415 nm. The dopants used to impart color in artificial simulants may be detectable as a complex rare-earth absorption spectrum, which is never seen in diamond.
   Section::::Possible colors.
  
  Diamonds occur in a variety of colors—steel gray, white, blue, yellow, orange, red, green, pink to purple, brown, and black. Colored diamonds contain interstitial impurities or structural defects that cause the coloration; pure diamonds are perfectly transparent and colorless. Diamonds are scientifically classed into two main "types" and several subtypes, according to the nature of impurities present and how these impurities affect light absorption:
   The clarity, or "purity", of a diamond refers to internal inclusions of the diamond, and is one of the 4-C's in determining a diamonds' value. Common "inclusions" that appear inside diamonds are black carbon spots and small cracks, commonly referred to as fractures or "feathers", due to their feathery whitish appearance when viewed from above or through the side. Diamonds may also have other inclusions such as air bubbles and mineral deposits such as iron or garnet. The size, color, and position of the inclusions are factors in determining the value of a diamond, especially when the other gemological characteristics are of a higher standard.
   Section::::Properties.:Hardness.
   Section::::Composites.
   Section::::Clarity enhancements.:Laser drilling.
  
  The development of laser drilling techniques have increased the ability to selectively target, remove and significantly reduce the visibility of black carbon inclusions on a microscopic scale. Diamonds containing hematite inclusions have been laser-drilled since the late 1960s, a technique credited to Louis Perlman that did a successful test a year after General Electric had made a similar one with a diamond for industrial use in 1962.
   Section::::Pigment.
  
  Carbon black (Color Index International, PBK-7) is the name of a common black pigment, traditionally produced from charring organic materials such as wood or bone. It appears black because it reflects very little light in the visible part of the spectrum, with an albedo near zero. The actual albedo varies depending on the source material and method of production. It is known by a variety of names, each of which reflects a traditional method for producing carbon black:
  
  BULLET::::- Ivory black was traditionally produced by charring ivory or bones (see bone char).
   Diamonds are made from carbon, usually graphite. Nevertheless, while a diamond is being formed, it may not totally crystallize, leading to the presence of small dots of black carbon. These black spots have been classified to be those of graphite, pyrrhotite and pentlandite. These surface flaws resemble a small black dot and may affect the clarity of the stone depending on the size of the imperfection. The occurrence of this kind of flaw is less common in diamonds compared to pinpoint inclusions. Carbons are usually seen in white or blue-white stones. Carbons are not commonly found in diamonds of poorer colors. Within the trade, these are called "carbon spots" and may be cleavage cracks which have developed through uneven heating or a blow. Cleavage cracks often appear to be dark or black in normal lighting conditions because of light reflection.
   Industrial diamonds are valued mostly for their hardness and heat conductivity, with the gemological qualities of clarity and color being mostly irrelevant. About 80% of mined diamonds (equal to about 100 million carats or 20 tonnes annually) are unsuitable for use as gemstones are relegated for industrial use (known as "bort)". synthetic diamonds, invented in the 1950s, found almost immediate industrial applications; 3 billion carats (600 tonnes) of synthetic diamond is produced annually.
   A small number of otherwise gem-quality stones that possess a brown body color can have their color significantly lightened or altogether removed by HPHT treatment, or, depending on the type of diamond, improve existing color to a more desirable saturation. The process was introduced by General Electric in 1999. Diamonds treated to become colorless are all Type IIa and owe their marring color to structural defects that arose during crystal growth, known as "plastic deformations", rather than to interstitial nitrogen impurities as is the case in most diamonds with brown color. HPHT treatment is believed to repair these deformations, and thus whiten the stone. (This is probably an incorrect conclusion, the whitening due to destruction of stable vacancy clusters according to one of the researchers). Type Ia diamonds, which have nitrogen impurities present in clusters that do not normally affect body color, can also have their color altered by HPHT. Some synthetic diamonds have also been given HPHT treatment to alter their optical properties and thus make them harder to differentiate from natural diamonds. Pressures of up to 70,000 atmospheres and temperatures of up to 2,000 °C (3,632 °F) are used in HPHT procedure.
   The majority of diamonds that are mined are in a range of pale yellow or brown color that is termed the "normal color range". Diamonds that are of intense yellow or brown, or any other color are called "fancy color" diamonds. Diamonds that are of the very highest purity are totally colorless, and appear a bright white. The degree to which diamonds exhibit body color is one of the four value factors by which diamonds are assessed. Diamonds have a color grading system that refers to the absence of color. This system goes from D to Z. The more colorless a diamond is, the rarer and more valuable it is because it appears white and brighter to the eye.
   Only a very small fraction of the diamond ore consists of actual diamonds. The ore is crushed, during which care has to be taken in order to prevent larger diamonds from being destroyed in this process and subsequently the particles are sorted by density. Today, diamonds are located in the diamond-rich density fraction with the help of X-ray fluorescence, after which the final sorting steps are done by hand. Before the use of X-rays became commonplace, the separation was done with grease belts; diamonds have a stronger tendency to stick to grease than the other minerals in the ore.
   The latest development is nano diamond coating, an extremely thin layer of diamond material. If not tested properly it may show the same characteristics as a diamond.
  
  A diamond's electrical conductance is only relevant to blue or gray-blue stones, because the interstitial boron responsible for their color also makes them semiconductors. Thus, a suspected blue diamond can be affirmed if it completes an electric circuit successfully.
  
  Section::::Artificial simulants.
   Both CVD and HPHT diamonds can be cut into gems and various colors can be produced: clear white, yellow, brown, blue, green and orange. The advent of synthetic gems on the market created major concerns in the diamond trading business, as a result of which special spectroscopic devices and techniques have been developed to distinguish synthetic and natural diamonds.
  
  Section::::History.
   Section::::Properties.:Bonding of DLC coatings.
   With the addition or elimination of certain impurities under controlled conditions, diamonds of various color can be produced. Since nitrogen is abundant in the atmosphere, the HPHT process is more likely to produce bright yellow diamonds than any other color (although natural yellow diamonds often have higher value than white diamonds). The yellow tint occurs when approximately five out of each 100,000 carbon atoms in the diamond crystal lattice are replaced with nitrogen atoms.
   Nitrogen is by far the most common impurity found in gem diamonds and is responsible for the yellow and brown color in diamonds. Boron is responsible for the blue color. Color in diamond has two additional sources: irradiation (usually by alpha particles), that causes the color in green diamonds, and plastic deformation of the diamond crystal lattice. Plastic deformation is the cause of color in some brown and perhaps pink and red diamonds. In order of increasing rarity, yellow diamond is followed by brown, colorless, then by blue, green, black, pink, orange, purple, and red. "Black", or Carbonado, diamonds are not truly black, but rather contain numerous dark inclusions that give the gems their dark appearance. Colored diamonds contain impurities or structural defects that cause the coloration, while pure or nearly pure diamonds are transparent and colorless. Most diamond impurities replace a carbon atom in the crystal lattice, known as a carbon flaw. The most common impurity, nitrogen, causes a slight to intense yellow coloration depending upon the type and concentration of nitrogen present. The Gemological Institute of America (GIA) classifies low saturation yellow and brown diamonds as diamonds in the "normal color range", and applies a grading scale from "D" (colorless) to "Z" (light yellow). Diamonds of a different color, such as blue, are called "fancy colored" diamonds and fall under a different grading scale.
   Above the triple point, the melting point of diamond increases slowly with increasing pressure; but at pressures of hundreds of GPa, it decreases. At high pressures, silicon and germanium have a BC8 body-centered cubic crystal structure, and a similar structure is predicted for carbon at high pressures. At , the transition is predicted to occur at . 
  
  Section::::Material properties.:Crystal structure.
   BULLET::::- Type Ib make up about 0.1% of all natural diamonds. They contain up to 0.05% (500 ppm) of nitrogen, but the impurities are more diffuse, the atoms are dispersed throughout the crystal in isolated sites. Type Ib diamonds absorb green light in addition to blue, and have a more intense or darker yellow or brown colour than Type Ia diamonds. The stones have an intense "yellow" or occasionally "brown" tint; the rare "canary" diamonds belong to this type, which represents only 0.1% of known natural diamonds. The visible absorption spectrum is gradual, without sharp absorption bands. Most blue-gray diamonds coming from the Argyle mine of Australia are not of type IIb, but of Ia type; those diamonds contain large concentrations of defects and impurities (especially hydrogen and nitrogen) and the origin of their color is yet uncertain. Almost all HPHT synthetic diamonds are of Type Ib.
   Inclusions trapped in diamond can reveal the material and conditions much deeper in the mantle. Large gem diamonds are usually formed in the transition zone part of the mantle, (410 to 660 km deep) and crystallise from a molten iron-nickel-carbon solution, that also contains sulfur and trace amounts of hydrogen, chromium, phosphorus and oxygen. Carbon atoms constitute about 12% of the melt (about 3% by mass). Inclusions of the crystallised metallic melt are sometimes included in diamonds. Diamond can be caused to precipitate from the liquid metal, by increasing pressure, or by adding sulfur.
  