Black diamond refers to both carbonado diamonds and black gem diamonds, they are not a diamond alternative and they are not synthetic diamonds. Carbonado, a rare type of diamond with a polycrystalline structure, is not normally considered a gemstone. Nevertheless, super large diamonds like large, faceted carbonados sell for several million dollars. Black gem diamonds, on the other hand, are a color variety of monocrystalline, or “single-crystal,” diamonds—the familiar stones we see in jewelry stores.

Carbonado Black Diamonds

In 1843, Brazilian placer miners discovered dense, opaque, black pebbles and cobbles that they named “carbonado,” after the Portuguese carbonizado, meaning “carbonized” or “burned” and alluding to their charred appearance. Mineralogists subsequently described carbonado as a previously unknown form of diamond with a polycrystalline structure and consisting of tightly bonded aggregates of randomly arranged diamond microcrystals.

Carbonado had no value until the 1870 introduction of diamond-studded drill bits. With its greater hardness and durability, along with a microcrystalline structure that provided more cutting edges, carbonado’s rock-cutting ability far exceeded that of a monocrystalline diamond.

Industrial demand for carbonado soared and, by 1880, Brazil was mining 70,000 carats (30.9 pounds) per year and selling it to the United States and Europe for $20 per carat. Carbonado-studded drill bits were later used extensively in building the Panama Canal and developing Minnesota’s great open-pit iron mines. Carbonado has now been replaced by synthetic polycrystalline diamond and is no longer mined commercially

The Great Carbonados

Carbonado diamonds are quite rare. Only an estimated three tons have been mined in the past 150 years—almost nothing compared with the 25 tons of monocrystalline diamonds now mined worldwide each year. Despite its scarcity, carbonado has provided many extraordinary specimens.

In 1895, Brazilian placer miner Sérgio Borges de Carvalho recovered a huge carbonado of 3,167 carats (22.34 ounces). Weighing 61 carats more than South Africa’s fabled Cullinan Diamond (monocrystalline), it was the largest diamond of any kind ever found. The “Sérgio Diamond,” named in de Carvalho’s honor, sold for $16,000 ($500,000 in 2023 dollars). Unfortunately, it was broken up into cutting studs for drill bits.

Of the few gems ever cut from Carbonado, the most spectacular is the Enigma Diamond. The world’s largest faceted diamond, the Enigma sold in 2022 in a highly publicized auction for $4.3 million. The preponderance of “fives” in this irregularly cut, 55-facet, 555.55-carat gem is not coincidental: Its previous owner, an Arab tycoon, styled its cut after the ancient Mideastern hamsa amulet, which both Jewish and Arabic traditions associate with the number five.

The Origin of Carbonado

Scientists initially assumed that both polycrystalline and monocrystalline diamonds formed in the extreme heat and pressure of the Earth’s mantle and were later emplaced in surface kimberlite pipes. But carbonado does not occur in association with monocrystalline diamonds.

By the 1970s, researchers had concluded that carbonado’s unusual inclusions indicated not mantle formation, but rather meteoric origin. They also noted that because carbonado in quantity was found only in Bahia, Brazil, and the Ubangi River region of the Central African Republic—and in the same geologic horizons—it had likely fallen to Earth in a single, massive meteoric event when South America and Africa were joined as one landmass.

Many scientists now believe that carbonado formed on exploding red giants (large stars with low surface temperatures) when shock waves compressed carbon into polycrystalline diamonds before hurling it into space where some eventually reached Earth as meteorites.

Black Diamonds

Meanwhile, as scientists continued to debate the origin of carbonado, black monocrystalline diamonds were gaining popularity as faceted gems. Their black color and opacity are caused by numerous tiny inclusions, most often of graphite or amorphous carbon.

Only about 1 in 10,000 monocrystalline diamonds is naturally black. Historically, these stones had no gem value until the 1990s when they began appearing in white gold and platinum settings accompanied by colorless melee diamonds. These black monocrystalline diamonds also began attracting metaphysical interest as stones that provide wearers with power, determination, and inner strength.

Natural vs. Treated

Faceted, natural, black monocrystalline diamonds now sell for about $2,500 per carat. But most black-diamond gems currently being sold started as heavily included, grayish, industrial-grade diamonds. Heating these low-value stones to 1300°C for several hours converts tiny inclusions of amorphous carbon to graphite which absorbs white light and produces nearly opaque, very dark green stones that appear black. Today, loose, heat-treated, faceted black diamonds sell for roughly $300 per carat.

The most celebrated natural, black, monocrystalline diamond gem is the 67.5-carat Black Orlov Diamond. Mined as a 195-carat rough crystal, it was believed to be cursed after three of its owners committed suicide. To break the curse, the gem was cut into three pieces, the largest being the Black Orlov. Mounted in a brooch and surrounded by a circle of 108 small, colorless diamonds, the Black Orlov has been displayed at major museums around the world.

So, whether as polycrystalline carbonado or monocrystalline gems, black diamonds are finally gaining the respect they deserve.

This story about black diamonds previously appeared in Rock & Gem magazine. Click here to subscribe. Story by Steve Voynick.

The post Black Diamonds Gain Respect first appeared on Rock & Gem Magazine.

January

Garnet has been the birthstone for January since the 15th century, at least. With a Mohs hardness of 6.5 to 7.5, it can be faceted into beautiful gemstones that wear well in jewelry. Since the term “garnet” actually refers to a group of nesosilicate gems, those born in this month can choose from a rainbow of colors.

The most common members are red almandine, an iron-aluminum silicate; red pyrope, a magnesium aluminum silicate; orange-yellow spessartine, a manganese aluminum silicate; the yellow or green varieties of andradite, a calcium-iron silicate; predominately green grossular, a calcium-aluminum silicate; and rare, bright-green uvarovite, a calcium chromium silicate.

February

From the 15th century to the present, amethyst has been the preferred birthstone for February. Amethyst belongs to a mineral family that can compete with garnet for diversity of color: quartz.

Pure quartz is colorless, as exemplified by Herkimer diamonds. The causes of amethyst’s shades of pale violet to rich purple are radiation and the inclusion of iron impurities and trace elements.

As a rule, amethyst crystals are short and stubby, and occur in large numbers, often filling a large vug a hollow petrified tree section, or lining the inside of a geode. Fine crystals that are large enough to produce a faceted gem of over 20 carats are rare.

March

The current choice of a birthstone for March is aquamarine. Aquamarine is a variety of beryl (Mohs 7.5-8). Its name was derived from the fact that the beautiful, transparent, blue-green coloration of the gem resembles that of seawater. It can be found in translucent to transparent crystals that form in the hexagonal system. The six-sided crystals are often striated lengthwise.

Aquamarine develops in metamorphic rocks and, more often, in pegmatites.

April

Before 1900, a person with an April birthday had two choices of birthstone: diamond or sapphire. During the 20th century, however, diamonds became the preferred stone.

Diamond, a mineral consisting of pure carbon, heads the list of all gemstones for its beauty and hardness. A 10 on the Mohs Scale of Hardness, it is resistant to scratching and is an ideal gem to set in rings. Its hardness results from the arrangement of its atoms in cubes.

All diamonds have slightly rounded faces, and they’re so smooth they feel greasy to the touch. They can be colorless and water clear to blue, pink, yellow, brown, green or black, and transparent or translucent. They shine with an adamantine luster when held to the light.

May

There were two choices for May birthstones for several hundred years: emerald and agate. The popularity of agate seems to have waned at the turn of the 20th century, so emerald is now the favorite. It’s the green member of the beryl family of gemstones. The color varies from bright green to pale green and, sometimes, darker shades of blue-green.

Fine emeralds have a velvety surface appearance and, in the better stones, an even distribution of color. One bad trait of emeralds is a tendency to have inclusions. It’s rare to find an emerald without some slight imperfection. This in no way deters from the beauty of this gemstone, though. It can also be one way of determining whether an emerald is a simulated gem or the real thing, as manmade stones have no imperfections.

June

The contemporary choices for June are pearl, moonstone and alexandrite. Of course, a pearl is the organic product of marine bivalves and not a mineral.

Moonstone is a variety of feldspar that shows adularescence, or schiller, an optical effect that produces a milky luster with a bluish tinge that appears to move across the stone when it is tilted. The phenomenon is named after the feldspar variety adularia.

Alexandrite is a color-change variety of chrysoberyl (beryllium aluminum oxide). This is a very rare and expensive gemstone. It has a hardness of 8.5, and its crystals are either tabular or prismatic. The distinction between alexandrite and chrysoberyl is simply color. A strange characteristic of alexandrite is that it is red, purple or violet when held under artificial light, but in daylight, it looks green.

July

Ruby is the standard birthstone for the month of July. It is a corundum (aluminum oxide) gem that gets its color from the presence of chromium in its structure. An exceptionally hard mineral, corundum illustrates a hardness of nine on the Mohs scale. “Pigeon-blood” red is the preferred color for rubies, though they also occur in lighter shades, including pink. All other colors of corundum are called sapphires.

Ruby exhibits all the desirable properties of a jewelry stone: beauty, durability, optical properties, and rarity. Some rubies display a star or asterism when fashioned into a cabochon. This effect is caused by the reflection of light from numerous inclusions of minute, needle-like crystals of rutile. Corundum crystallizes in the hexagonal system with a tabular-barrel-shaped habit.

August

Current birthstones for August are peridot, the gem-quality form of olivine and spinel. Olivine makes up a large portion of the earth’s mantle. Rocks containing olivine have been brought to the surface by volcanic action and actually blown out in the form of volcanic bombs. Masses of olivine have been found in meteorites, and the Apollo astronauts brought basaltic rocks back from the moon that contained olivine.

A popular jewelry stone, peridot has a hardness of 6.5-7 and can be transparent or translucent, with a vitreous luster. Its color shades from deep green to apple green, yellow-green or olive. It’s most often found in granular nodules, forming short, prismatic crystals in the orthorhombic system.

Spinel is the gem-quality member of the larger spinel group. Its hardness (Mohs 7.5-8.0) makes it ideal for jewelry use. Its spectrum of colors includes red, pink, purple, blue and lavender. In times past, red spinel was often mistaken for ruby. A notable example is the Black Prince’s Ruby, set in the royal crown of England.

September

The birthstone for September is sapphire. This term refers to any corundum (aluminum oxide) gem that has any color other than red (ruby). Sapphires may be colorless, blue, green, yellow, orange, brown, pink, purple, gray, black, or multicolor. At Mohs 9, its hardness is second only to that of a diamond.

Heat treatment is sometimes used to give natural blue sapphires a deeper, more pleasing color. Natural star sapphires, which display the optical phenomenon of asterism, are very rare.

October

Two options for October are opal and tourmaline. Opal is a magnificent gemstone with a play of color or “fire” in all colors of the spectrum. Spaces between the tiny spherules of silica that make up the gem diffract light into its spectral colors. Red, yellow, green and blue, in strong to pastel shades, flash from the stone when it is tilted.

Opal occurs in common and precious types. Common opal does not display any reflective fire. It may have a honey-yellow, brown, gray or colorless body color that is milky and opaque. Opal (Mohs 5-6) is not a very hard gemstone.

Tourmaline, a silicate of boron, has a complicated chemical composition, in which a number of elements, including calcium, iron, sodium and aluminum, may combine. It has a Mohs hardness of 7-7.5.

It belongs to the trigonal crystal system and its habit is hemimorphic (a crystal having two ends of an axes unlike in its planes).

Because of the coloration of the individual stones, tourmaline has several names, including schorl (black), rubellite (red), indicolite (blue), and dravite (brown). Tricolor crystals are common. The popular watermelon variety has an outer layer of green around a red core.

November

The current birthstones for November are topaz and citrine. People tend to think of topaz, a silicate mineral with aluminum and fluorine, as a yellow stone, but heat-treating and color-enhancing adaptations have made blue the predominant color on the market. It is an allochromatic mineral, which means its color is caused by internal defects in the crystal and has a Mohs hardness of eight.

Citrine is the golden member of the quartz family (silicon dioxide). Though quartz in its many forms is one of the most abundant minerals on earth, fine, gem-grade crystals are not that common. Citrine is affordable and, when faceted, rivals more expensive gemstones in beauty.

December

There are three birthstones for December: turquoise, blue zircon and tanzanite. Turquoise (hydrated copper aluminum phosphate) is an opaque, blue-to-green, massive gem material. It has a relatively low hardness of Mohs 5-6, so care must be taken with turquoise jewelry.

The rarest and most valuable variety is robin’s-egg blue with black “spiderweb” veins of limonite. Fake turquoise, consisting of dyed howlite or magnesite, is common. Buyer beware.

Zircon (zirconium silicate) can be blue, black, red, brown, green, yellow, smoky, or water-clear. It has an adamantine luster much like that of a diamond, and it is often misidentified as such.

Tanzanite, the blue/purple variety of zoisite (basic calcium aluminum silicate), is a recently introduced alternative for December. Tanzanite crystals in shades of yellow to brown, green, pink, gray or blue are often heat-treated to produce a gemstone that is a beautiful and permanent blue.

This story about what are birthstones by month previously appeared in Rock & Gem magazine. Click here to subscribe! Story by Kenneth H. Rohn.

The post What are the Birthstones by Month? first appeared on Rock & Gem Magazine.

Super-large diamonds have been making big headlines. That’s because mines in southern Africa are yielding some of the biggest diamonds ever found. In January 2018, London-based Gem Diamonds, Ltd., announced the recovery of a 910-carat diamond at its Letšeng mine, in the nation of Lesotho. According to gem experts, this tennis ball-size stone, the fifth-largest diamond on record, will sell for a whopping $40 million, or nearly $44,000 per carat.

Presence of Super-Large Diamonds

But super-large diamonds may not be quite as rare as previously thought. In just the last two years, the Letšeng mine has also yielded stones weighing 603 and 530 carats, along with four other stones weighing 300 carats or more.

Another source of super-large diamonds is Botswana’s Karowe mine. In 2015, Karowe’s owner, Lucara Diamond Corp., based in Vancouver, Canada, announced the recovery of a 1,110-carat diamond measuring 2.6 in. x 2.3 in. x 1.8 in.—the world’s second-largest diamond. Since then, Karowe has also yielded stones of 812 and 374 carats.

More super-large diamonds have been mined in the past 10 years than throughout history. They come from African mines that are using state-of-the-art, diamond-detection systems.

Diamond Formation

Diamonds form in Earth’s mantle at depths of about 200 miles and in conditions of extreme temperature and pressure. Some are carried to the surface in columns of kimberlitic magma that solidify as narrow, vertical, kimberlite pipes. Only 1% of these pipes are diamondiferous, and only a few of these are rich enough to mine. Kimberlite ores containing 1 carat of diamond per ton are considered high-grade.

In diamondiferous kimberlite, ore grade and diamond size are often inversely proportional. Higher-grade ore yields smaller diamonds, and vice versa.

The ore at the Karowe mine, which has produced more than half the world’s diamonds weighing more than 100 carats, grades only 0.16 carat per ton. But Karowe’s relatively few diamonds tend to be unusually large. While rough diamonds of less than 1 carat sell for as little as $20 per carat, Karowe’s 1,110-carat diamond, yet to be sold, could bring $70 million, or $63,000 per carat.

Loss of Super-Large Specimens

Most of southern Africa’s kimberlite mines are huge, mechanized open pits, where ore is drilled, blasted, crushed to 6 inches in size, and fine-crushed to 1 inch. The crushed ore is concentrated in a dense media separation (DMS) process (diamond is denser than most other kimberlite components). X-ray beams then cause the diamonds to fluoresce, enabling light-sensitive separating devices to “kick” the fluorescing diamonds from the conveyor streams of crushed ore.

But it now appears that certain African mines that are proven sources of big stones have unknowingly been losing super-large diamonds. And the loss of just one giant stone represents tens of millions of dollars in lost earnings.

To prevent this loss, mines have installed powerful X-ray units to scan kimberlite ore before the first crushing step. X-rays can reveal density differentials that may indicate the presence of large diamonds, even those completely hidden within chunks of kimberlite.

These industrial X-ray units and the computers needed to instantly interpret their scanning data are not cheap, but as the rapidly growing numbers of super-large diamond recoveries indicate, they are worth every penny.

Attention on Rarity

The theory that the rarity of super-large diamonds may have been overestimated is focusing attention on the legendary Cullinan diamond. The 3,106-carat Cullinan, mined in 1905 at South Africa’s Premier mine, is still the largest diamond ever found. It was cut into nine major stones—the 530-carat Star of Africa, the 317-carat Second Star of Africa, and seven other large gems—and 96 “minor brilliants”.

Noting the sharp increase in recoveries of super-large diamonds, some experts suggest that in the not-distant future, the legendary Cullinan just might become the world’s second-largest diamond.

This story about digging for amethyst stones appeared in a previous issue of Rock & Gem magazine. Click here to subscribe! Story and photos by Steve Voynick. 

The post The Era of Super-Large Diamonds first appeared on Rock & Gem Magazine.

They say diamonds are judged by the 4Cs: color, clarity, cut, and carat weight. But when a new diamond is dug up, all everyone seems to focus on is carats. And so it is with the latest big discovery out of Botswana.

Weighing in at 1,174 carats, this stone is said to be the third-largest recorded gem-quality diamond ever found. Photos of people holding it show it to be as large as a juice glass, or big enough to “fill the palm of a large hand,” per one report. Its exact dimensions, per a company press release, are 77x55x33mm.

The diamond was recovered after material mined from a kimberlite deposit went through a primary crusher, and it is believed that the original stone may have weighed in excess of 2,000 carats before the rough material entered the crusher. Why do they believe this is so? Three other diamonds with very similar characteristics were recovered at the same time weighing 471 carats, 218 carats, and 159 carats. All are believed to have been part of one stone.

The stone is a clear or “white” diamond. It was discovered on June 12, 2021, by the Lucara Botswana division of Lucara Diamond Corp. of Canada at the Karowe Diamond Mine and was subsequently presented to the Botswana government in a July 7 ceremony that included President Mokgweetsi Masisi. By July 19, the stone was residing in Antwerp, the diamond processing capital of the world, to be examined, analyzed, and valued over the next four to six months. (Preliminary estimates put the value of the stone at tens of millions of dollars.) From Antwerp, it will head to New York City as part of a world tour before the stone is ultimately cleaved into smaller cut stones. An official name for the diamond is yet to be chosen.

Botswana has eclipsed South Africa as the leading diamond producer on the African continent. In fact, it is said that Botswana alone accounts for six of the top ten raw diamonds ever discovered! By the way, this latest find follows close on the heels of the June 1 discovery of a 1,098 carat diamond by the Botswana diamond firm Debswana. Ever-so-briefly, it was the third largest diamond ever found.

For the record, the largest raw diamond ever found? That would be the 3,106-carat Cullinan Diamond dug up in South Africa back in 1905 and cut into pieces to join the Crown Jewels of Great Britain. The second-largest diamond? A 1,758-carat stone called the Sewelô also found in Botswana’s Karowe Diamond Mine in 2019.

The post Botswana Produces the World’s Third-Largest Diamond first appeared on Rock & Gem Magazine.

The diamond is one fabled gemstone! For example, google “Hope Diamond” to see all the legends associated with just this one stone said to bring misfortune to its owners. So much lore has grown up around diamonds that it would fill the pages of this magazine for the rest of the year to capture even a portion. Jack Ogden wrote a book about this very topic, published in 2018, Diamonds: An Early History of the King of Gems. I’ll relate just two of the many facts—and fictions—Ogden explores, along with other myths and legends.

Per Ogden, diamond mining originated in India. Most specimens came from riverbeds, where they were found in gravel. The Valley of Gems was especially renowned, but there was a problem: it had sheer cliffs and was filled with poisonous snakes!

Legend says locals tossed meat into the valley. Eagles snatched up pieces along with diamonds that stuck to the meat. All that was left to do was collect diamonds from the eagles’ nests, although I’m not sure which is more daring: confronting poisonous snakes or a mad eagle!

Because they are the hardest of minerals, diamonds proved impossible to cut, so the earliest diamonds in jewelry were stones of a natural octahedral shape. Some preferred it that way. They claimed altering a diamond destroys its magic powers. Eventually, cleaving, shaping, and polishing methods were developed, but such methods were closely kept secrets and, as Ogden relates, rumors began to emerge. One was that diamonds could be cut, but only if soaked in goat blood!

Ancient Greeks thought diamonds protected against poison and evil, whereas Hindus thought a flawed stone could invite misfortune.

In general, diamonds were viewed as symbols of wisdom, self-confidence, and power, probably because only powerful rulers could afford them. Today, they are used in engagement rings to signify enduring love, and they mark 60th anniversaries or a “diamond jubilee.” If you were lucky enough to be born in April, a diamond is your birthstone!

Many more legends abound around diamonds in general and individual stones: the Hope Diamond, the Blue Diamond of the Crown, the Koh-i-Noor, the Shah Diamond, the Regent Diamond, the Cullinan I and II, the Tiffany Diamond, and the Sancy Diamond, among others. Some are famous for long histories and owners who have included sultans and slaves, kings and queens, industry titans and movie stars. Still others are infamous for legendary curses and daring thefts.

All photos courtesy Jim Brace-Thompson.

The post A Luxury Gem Steeped in Fact & Fable first appeared on Rock & Gem Magazine.