Carbonado, black diamond💣💣💥💥

 Carbonado, commonly known as black diamond, is one of the toughest forms of natural diamond. It is an impure, high-density, micro-porous form of polycrystalline diamond consisting of diamond, graphite, and amorphous carbon, with minor crystalline precipitates filling pores and occasional reduced metal inclusions.[1] Titanium nitride (TiN, osbornite) has been found in carbonado.[2] It is found primarily in alluvial deposits where it is most prominent in mid-elevation equatorial regions such as Central African Republic and in Brazil, where the vast majority of carbonado diamondites have been found. Its natural colour is black or dark grey, and it is more porous than other diamonds.

Unusual properties:

Carbonado diamonds are typically pea-sized or larger porous aggregates of many tiny black crystals. The most characteristic carbonados are mined in the Central African Republic and in Brazil, in neither place associated with kimberlite, the source of typical gem diamonds. Lead isotope analyses have been interpreted as documenting crystallization of carbonados about 3 billion years ago; yet carbonado is found in younger sedimentary rocks.

Mineral grains included within diamonds have been studied extensively for clues to diamond origin. Some typical diamonds contain inclusions of common mantle minerals such as pyrope and forsterite, but such mantle minerals have not been observed in carbonado. In contrast, some carbonados contain authigenic inclusions of minerals characteristic of the Earth's crust; the inclusions do not necessarily establish formation of the diamonds in the crust, because while the obvious crystal inclusions occur in the pores that are common in carbonados, they may have been introduced after carbonado formation. Inclusions of other minerals, rare or nearly absent in the Earth's crust, are found at least partly incorporated in diamond, not just in pores: among such other minerals are those with compositions of Si, SiC, and Fe‑Ni. No distinctive high-pressure minerals, including the hexagonal carbon polymorph, lonsdaleite, have been found as inclusions in carbonados although such inclusions might be expected if carbonados formed by meteorite impact.

Isotope studies have yielded further clues to carbonado origin. The carbon isotope value is very low (little carbon‑13 compared to carbon‑12, relative to typical diamonds).

Carbonado exhibits strong luminescence (photoluminescence and cathodoluminescence) induced by nitrogen and by vacancies 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,[4] 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 last longer and require less maintenance. Carbonado was recognized as an 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. 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."

Hypotheses for origin:

The origin of carbonado is controversial, and some proposed hypotheses are as follows:

Direct conversion of organic carbon under high-pressure conditions in the Earth's interior, the most common hypothesis for diamond formation

Shock metamorphism induced by meteoritic impact at the Earth's surface

Radiation-induced diamond formation by spontaneous fission of uranium and thorium

Accumulated local formation in reduced organic-rich sediment over long geologic periods due to pyrometamorphic-rapid processes associated with long-duration superbolt lightning strikes, known to have similar global distribution as carbonado diamondite deposits at similar elevations.

Formation inside an earlier-generation giant star in our area, that long ago exploded in a supernova.

An origin in interstellar space, due to the impact of an asteroid, rather than being thrown from within an exploding star.

The origin of carbonado is still under debate.

Extraterrestrial origin hypothesis:

Supporters of an extraterrestrial origin of carbonados such as Stephen Haggerty propose that their material source was a supernova which occurred at least 3.8 billion years ago. After coalescing and drifting through outer space for about one and a half billion years, a large mass fell to earth as a meteorite 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 split into Brazil and the Central African Republic, assumed to be the only two known locations of carbonado-diamond deposits.

The presence of osbornite, which only forms under very reducing conditions and at very high temperatures, argues for an extraterrestrial origin.

Largest cut diamond:

The largest cut black diamond in the world is a carbonado named 'The Enigma', weighing 555.55 carats (111 g).

See also:

Minerals portal

Amsterdam Diamond – 6.748 g carbonado diamond, with 145 facets, in a pear shape, cut from a 11.17 g rough

Bort – Shards of non-gem-quality diamonds

Korloff Noir – Black diamond

Material properties of diamond

Popigai diamonds – Impact crater in Siberia, Russia

Sergio (carbonado) – Largest known rough diamond

Spirit of de Grisogono Diamond – World's largest cut black diamond

Superhard material – Material with Vickers hardness exceeding 40 gigapascals

Solar eclipse of April 8, 2024💣💫

^^^^^A total solar eclipse will take place at the Moon's ascending node on Monday, April 8, 2024, visible across North America and dubbed the Great North American Eclipse (also Great American Total Solar Eclipse and Great American Eclipse) by some of the media.[1][2][3] A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby obscuring the image of the Sun for a viewer on Earth. A total solar eclipse occurs when the Moon's apparent diameter is larger than the Sun's, blocking all direct sunlight, turning day into darkness. Totality occurs only in a narrow path across Earth's surface, with the partial solar eclipse visible over a surrounding region thousands of kilometres wide.

Occurring only one day after perigee (perigee on Sunday, April 7, 2024), the Moon's apparent diameter will be 5.5% larger than average. With a magnitude of 1.0566, its longest duration of totality will be of 4 minutes and 28.13 seconds near the Mexican town of Nazas, Durango, (about 4 mi (6 km) north), and the nearby city of Torreón, Coahuila.

This eclipse will be the first total solar eclipse to be visible in the provinces of Canada since February 26, 1979,[4][5] the first in Mexico since July 11, 1991,[6] and the first in the U.S. since August 21, 2017. It will be the only total solar eclipse in the 21st century where totality will be visible in Mexico, the United States, and Canada.[7] It will also be the last total solar eclipse visible in the Contiguous United States until August 23, 2044.

The final solar eclipse of the year will occur six months later, on October 2, 2024.

Cloud-cover prospects along the path:

April is a month of changeable weather along the eclipse path. The weather in Mexico and the southern United States include afternoon convective buildups, whereas northern regions are still immersed in late winter and early spring weather, with passing low-pressure disturbances (e.g., rain, snow). Of these disturbances, eclipse-day cloud cover is most likely, unless severe storms are present across the south or spring storms with blizzard-like conditions are passing in the north. Cloud patterns are simple: lowest average cloud coverage occur in the south, particularly in Mexico, whereas the highest amounts of coverage crop up in the northeastern United States and Canada.[16]

Along the eclipse path, various locations will encounter differing cloud coverage and thus different views. Cloud cover is measured by satellite and averages 25–35% along the axis of the eclipse track—from Mazatlán, Sinaloa, to Torreón, Coahuila—and begins a steady increase, rising above fifty percent along the U.S.-Mexico border. At Carbondale, Illinois, where the 2024 track crosses that of the solar eclipse of August 21, 2017, average cloudiness rises to sixty percent before it peaks at seventy-five percent in western Ohio.

The Great Lakes Erie and Ontario influence cloud cover along the eclipse central line, and the percentage of cover declines to 60–65% through Cleveland, OH; Buffalo, NY; and Rochester, NY. Through Vermont, Quebec, Maine, and New Brunswick, April cloudiness climbs to a maximum of eighty percent or more, before declining by about fifteen percent along the shores of the Gulf of St. Lawrence. The community of Tignish, Prince Edward Island, enjoys the best cloud-cover prospects in the northeast due to its exposure to the Gulf, with average monthly amounts falling back to sixty-five percent. Farther across the Gulf of St. Lawrence, April cloudiness climbs again. Newfoundland, standing in the path followed most often by April storms, sees an average monthly cloud cover that peaks between 80 and 85%.

Maps of average cloud cover identify a few locations off the central axis of the eclipse where cloud cover is more favorable to the eclipse traveler. The western side of the track through Texas has sunnier skies than those on the eastern side. The same is true in Arkansas and Missouri, where average April cloud cover can be as much as 20 percent lower than on the east side, around Jonesboro. Through New York, Vermont, and Maine, heavier cloud tends to favor higher terrain, though the differences across the shadow path are not large, as these states already have a large average cloud cover in springtime.

#diamondring