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structure_minerals
Mixed gemstone lots have been restocked - Limited quantity available, link in bio
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Ruby, Sapphire, Tourmaline, Topaz, Apatite, Garnet, Rhodizite, Amethyst, Quartz, Peridot, Grape Agate, Orange Kyanite, Vesuvianite, and more✨
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Relaxing on Green Sandy Beaches
What better way to escape than to travel to Hawai'i and kick off our shoes on a green sandy beach?
Green beaches are pretty rare; in fact, there are only four of them in the world. They're formed by olivine crystals that have eroded from cinder cones. For example, Papakolea beach in Hawai'i is composed of eroded olivine particles from a 49,000 year old cinder cone. Olivine is created when basalt lava is high in magnesium and iron. These two elements are rather heavy for sand, so they are left behind when other sand particles are carried away by waves, leaving green beaches. Olivine is very common in the mantle of the earth and throughout space. When Apollo 15 returned to earth they brought back a sample of lunar olivine. In addition, weathered olivine on Mars might be an indication that there was once water on the planet; olivine weathers quickly, leaving idingsite, a combination of clay minerals, iron oxides and ferrihydrites
Because olivine is so prevalent in Hawaiian lavas and because olivine is one of the first crystals to form as magma cools, it is often considered the "Hawaiian Diamond". When olivine is at its finest (or most pure), it forms the gem we call peridot.
Further reading: https://www.facebook.com/TheEarthStory/posts/511311338929915 Further reading on peridot:https://www.facebook.com/TheEarthStory/posts/555689177825464 Further reading: http://www.geologyin.com/2014/11/the-green-sand-beach-mahana-beach.html Picture of Papakolea Beach courtesy of: jonny-mthttp://commons.wikimedia.org/wiki/File:Papakolea_snapshot.jpg Olivine sand grain picture: photo © Brian W. Schallerhttp://en.wikipedia.org/wiki/File:A178,_Hawaii,_USA,_Papakolea_Green_Sand_Beach,_handful_of_sand,_2007.JPG
-Colter
Peridot and ludwigite Not all the gem olivine out there has its origins in the mantle, some form in high temperature contact metamorphic deposits, when hot olivine rich magmas interact with the country rocks that they intrude. The deep green gemmy specimen in the photo bears a testimony to this origin, in the form of dark needles of the rare magnesium-iron borate mineral Ludwigite. The latter often forms when the magma meets carbonate rocks, producing a diverse metamorphic mineral assemblage known under the umbrella term skarn. Mined in the Maran-Kagan valley of Pakistan, the specimen in the photo measures 3.1 x 2 x .9 cm and has been exhibited in several places as part of the now dispersed Herb Obodda collection. Our past posts on peridot: http://tinyurl.com/pavuvbqand http://tinyurl.com/n9hpgqu. Loz Image credit: Rob Lavinsky/iRocks.com http://www.mindat.org/min-2454.html http://webmineral.com/data/Ludwigite.shtml
Peridot and Ludwigite
Olivine (of which Peridot is the gemmy version) is a common mantle mineral, found on the surface in volcanic and exposed mantle rocks. It also sometimes occurs as beautiful green to brown crystals large enough to be faceted as gems, and its deep origins could induce one poetically to view it as our world's crystallised ichor. Known since antiquity, The traditional locale was St John's Island (aka Zabargad), off the Egyptian coast in the Mediterranean. In this place, a piece of Tethys oceanic crust was pushed up out of the mantle during Africa's ongoing collision with Europe, bringing its gems along with it. The earliest record of it being mined here dates from 70CE, and all the antique stones found in jewellery and crowns all over Europe came from Zabargad, though they were often mis-named as emerald. Known as Chrysolite in the ancient Greek world, ancient Egyptians prised it as the gem of the sun, and historians have speculated that Cleopatra's famous emeralds were olivine rather than beryl.
Hawaii was another historical source, where it was known as Pele's tears. It is now mostly mined out, though the cinder cone called Diamond Head was renowned for its crystals (see our past athttp://tinyurl.com/luex5gz). The grains at the famous Papakolea greensand beach near Hilo (covered athttp://tinyurl.com/q2f9zgz) are sand sized peridot crystals. The most valued colour is a bright olive green, with extra iron content increasing the brown component. The origin of the name is uncertain, but it is one of the birthstones for August, accounting for its continuing popularity.
The main current source remains Arizona, where it occurs as phenocrysts (large crystals that grew slowly before eruption) in a layer of basaltic lava at the top of Peridot Mesa on the San Carlos Apache Reservation. Only inhabitants are allowed to mine it, either in weathered out form gathered in gullies or by drilling and blasting. Other significant sources are Pakistan, China and Burma where it occurs as phenocrysts in basalts or as mantle xenoliths (foreign rocks) carried up by erupting lavas.
There is another amazing source: 4.5 billion year old crystals of peridot from pallassitic meteorites have been occasionally faceted and marketed with this extra cachet. It used to be thought they came from an asteroid's core-mantle boundary, but recent research suggests that they were formed during shattering collisions in the asteroid belt (see our post at http://tinyurl.com/mnhvap8)
Not all the gem olivine out there has its origins in the mantle however, some form in high temperature contact metamorphic deposits, when hot olivine rich magmas interact with the country rocks that they intrude. The deep green gemmy specimen in the photo bears a testimony to this origin, in the form of dark needles of the rare magnesium-iron borate mineral Ludwigite. The latter often forms when such magma meets carbonate rocks, producing a diverse metamorphic mineral assemblage known under the umbrella term skarn. Mined in Pakistan, the specimen in the photo measures 5.3 x 2.1 x 1.4 cm. Ludwigite forms in high temperature magnesium and iron rich skarns, and was first described in 1874 from the type locality in Romania and named after the Austrian chemist at Vienna university who first analysed it. It is naturally ferromagnetic and can form permanent magnets. In this case it consists of needle shaped (known as acicular) black crystals within the gemmy green peridot.
Loz
Peridot and Ludwigite
Olivine (of which Peridot is the gemmy version) is a common mantle mineral, found on the surface in volcanic and exposed mantle rocks. It also sometimes occurs as beautiful green to brown crystals large enough to be faceted as gems, and its deep origins could induce one poetically to view it as our world's crystallised ichor. Known since antiquity, The traditional locale was St John's Island (aka Zabargad), off the Egyptian coast in the Mediterranean. In this place, a piece of Tethys oceanic crust was pushed up out of the mantle during Africa's ongoing collision with Europe, bringing its gems along with it. The earliest record of it being mined here dates from 70CE, and all the antique stones found in jewellery and crowns all over Europe came from Zabargad, though they were often mis-named as emerald. Known as Chrysolite in the ancient Greek world, ancient Egyptians prised it as the gem of the sun, and historians have speculated that Cleopatra's famous emeralds were olivine rather than beryl.
Hawaii was another historical source, where it was known as Pele's tears. It is now mostly mined out, though the cinder cone called Diamond Head was renowned for its crystals (see our past athttp://tinyurl.com/luex5gz). The grains at the famous Papakolea greensand beach near Hilo (covered athttp://tinyurl.com/q2f9zgz) are sand sized peridot crystals. The most valued colour is a bright olive green, with extra iron content increasing the brown component. The origin of the name is uncertain, but it is one of the birthstones for August, accounting for its continuing popularity.
The main current source remains Arizona, where it occurs as phenocrysts (large crystals that grew slowly before eruption) in a layer of basaltic lava at the top of Peridot Mesa on the San Carlos Apache Reservation. Only inhabitants are allowed to mine it, either in weathered out form gathered in gullies or by drilling and blasting. Other significant sources are Pakistan, China and Burma where it occurs as phenocrysts in basalts or as mantle xenoliths (foreign rocks) carried up by erupting lavas.
There is another amazing source: 4.5 billion year old crystals of peridot from pallassitic meteorites have been occasionally faceted and marketed with this extra cachet. It used to be thought they came from an asteroid's core-mantle boundary, but recent research suggests that they were formed during shattering collisions in the asteroid belt (see our post at http://tinyurl.com/mnhvap8)
Not all the gem olivine out there has its origins in the mantle however, some form in high temperature contact metamorphic deposits, when hot olivine rich magmas interact with the country rocks that they intrude. The deep green gemmy specimen in the photo bears a testimony to this origin, in the form of dark needles of the rare magnesium-iron borate mineral Ludwigite. The latter often forms when such magma meets carbonate rocks, producing a diverse metamorphic mineral assemblage known under the umbrella term skarn. Mined in Pakistan, the specimen in the photo measures 5.3 x 2.1 x 1.4 cm. Ludwigite forms in high temperature magnesium and iron rich skarns, and was first described in 1874 from the type locality in Romania and named after the Austrian chemist at Vienna university who first analysed it. It is naturally ferromagnetic and can form permanent magnets. In this case it consists of needle shaped (known as acicular) black crystals within the gemmy green peridot.
Loz
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A gem in the sea
In the Red Sea where continents are literally breaking up and a new ocean is slowing extending lies Zabargad island, a massive piece of uplifted mantle. Rocks of this exposed mantle consist of fresh, non-serpentized peridiotites, mainly made of forsteritic olivine, including gem quality peridot. Of these, the peridot was crystalized in situ (therefore very fresh) in fault cracks that could have been 25m deep. Some of them can be over 1m in size! Although peridot is quite common worldwide, such large green gem crystals are only found at Zabargad.
In ancient times the island was was mined for topaz (before the 18th century peridot was one of several things named topaz) by the Greeks and the Egyptians, who called the island Topazios. It is believed that the name topaz actually derived firsthand from the island. According to Pliny’s Naturalis Historia, the Theban queen Berenice was presented the first specimen of topaz around 300 BC. In addition to Topazios, the island is also known as Seberged, Zebirget and St John’s Island. The name Zabargad is translated as peridot in Arabic.
From below the island appears as a pillar that rises from the sea, this is due to a incredibly blue lagoon with a steep reef that surrounds the island. These cliffs plunge down 500m and are a very popular place to dive.
Our past post on gem peridot:http://tinyurl.com/pavuvbq
-OW-
Image: Courtesy of Tim Priest. The north side of Zabargad with the steep cliffs on the foreground. Note the green color of the hills.
References: http://giantcrystals.strahlen.org/africa/seberged.htm http://www.palagems.com/peridot_buyers_guide.htm http://www.palagems.com/gem_news_2010_v3.php[_
_](https://www.facebook.com/TheEarthStory/photos/a.352867368107647/678275538900160/?type=3&theater#)
It was supposed to be three or four random ideas on monochromatic themes but then I thought might as well do a whole rainbow (which had to be seven because I like it better than six and that meant pink was also in since I like to spite Newton and not do indigo ever… though now I feel bad for indicolite)
In order - Garnet, quartz/agate, wulfenite, peridot, euclase, polybasite and morganite.
physicsfun Peridotite Xenoliths: here before you are chunks of Earth's mantle material from 50 kilometers or deeper below the surface, far below the deepest hole ever drilled at 12.3 km (a great effort which didn't even break through to the mantle). However, green peridotite crystals of olivine and pyroxenes are sometimes brought to the surface by viscous lava in the form of xenoliths- inclusions in the volcanic basalt as seen in this sample. This piece was collected from Peridot Mesa in the San Carlos Volcanic Field of AZ. Amazing sample of the inaccessible Earth's interior
You don’t need to go on a Jules Verne journey down to the center of the Earth, sometimes the center of the Earth is brought up to us!
These rocks are examples of peridotite xenoliths. A xenolith is a fragment of rock that becomes enveloped by magma without being melted or incorporated into it. In these photos, there are abundant fragments of xenolith peridotite surrounded by basalt. Peridotite is a rock composed of the minerals olivine and pyroxene, and it is the dominant rock composing the upper-part of Earth’s mantle.
As this basaltic magma was quickly rising through the mantle and the crust, it tore away solid chunks of mantle and brought them up in-tact to the surface. So when you look at these xenoliths, you’re looking at the composition of the Earth at tens to hundreds of kilometers depth!
These samples come from the San Carlos volcanic field near the town of Peridot, AZ. (Gem-quality olivine is called ‘peridot,’ so you can see where the town gets its name!) The San Carlos volcanic field covers a 50 km2 area of cinder cones and lava flows and is one of the world’s leading sources in gem-quality peridot.
All images by author
Peridot - Sapat Gali, Naran-Kagan Valley, Kohistan District, North-West Frontier Province, Pakistan
Peridot
Peridot
Olivine is a common mantle mineral found on the surface in volcanic and exposed mantle rocks. It also sometimes occurs as beautiful green to brown crystals large enough to be faceted as gems, and its deep origins could induce one poetically to view it as our world's crystallised ichor. We covered the mineral before at http://tinyurl.com/luxg9gc.
Known since antiquity, this specimen comes from the traditional locale of St John's Island (aka Zabargad), off the Egyptian coast in the Mediterranean. In this locale, a piece of Tethys oceanic crust was pushed up out of the mantle during Africa's ongoing collision with Europe, bring ing its gems along with it. The earliest record of it being mined here dates from 70CE, and all the antique stones found in jewellery and crowns all over Europe came from Zabargad, though they were were often mis-named as emerald. Known as Chrysolite in the ancient Greek world, ancient Egyptians prised it as the gem of the sun, and historians have speculated that Cleopatra's famous emeralds were olivine rather than beryl.
Hawaii was another historical source, where it was known as Pele's tears. It is now mostly mined out, though the cinder cone called Diamond Head was renowned for its crystals (see our pst at http://tinyurl.com/luex5gz). The grains at the famous Papakolea greensand beach near Hilo (covered at http://tinyurl.com/q2f9zgz) are sand sized peridot crystals.
The most valued colour is a bright olive green, with extra iron content increasing the brown component. The origin of the name is uncertain, but it is one of the birthstones for August, accounting for its continuing popularity.
The main current source remains Arizona, where it occurs as phenocrysts (large crystals that grew slowly before eruption) in a layer of basaltic lava at the top of Peridot Mesa on the San Carlos Apache Reservation. Only inhabitants are allowed to mine it, either in weathered out form gathered in gullies or by drilling and blasting. Other significant sources are Pakistan, China and Burma where it occurs as phenocrysts in basalts or as mantle xenoliths (foreign rocks) carried up by erupting lavas.
There is another amazing source: 4.5 billion year old crystals of peridot from pallassitic meteorites have been occasionally faceted and marketed with this extra cachet. It used to be thought they came from an asteroid's core-mantle boundary, but recent research suggests that they were formed during shattering collisions in the asteroid belt (see our post at http://tinyurl.com/mnhvap8)
Loz
Image credit, size of piece 2.4 x 2 x .6 cm: Rob Lavinsky/iRocks.com http://www.gia.edu/peridot http://webmineral.com/data/Olivine.shtml#.Ug_Xim2O64w http://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/peridot.html
Peridot
Olivine is a common mantle mineral found on the surface in volcanic and exposed mantle rocks. It also sometimes occurs as beautiful green to brown crystals large enough to be faceted as gems, and its deep origins could induce one poetically to view it as our world's crystallised ichor.
Known since antiquity, this 2.7 x 2.2 x 1.6 cm specimen (perched atop a silvery gret dodecahedral crystal of the dense iron oxide mineral magnetite) comes from Pakistan, but the traditional source was St John's Island (aka Zabargad), off the Egyptian coast in the Mediterranean. In this locale, a piece of Tethys oceanic crust was pushed up out of the mantle during Africa's ongoing collision with Europe, bringing its mantle and crystallised gems along with it. The earliest record of it being mined here dates from 70CE, and all the antique stones found in jewellery and crowns all over Europe came from Zabargad, though they were were often mis-named as emerald. Known as Chrysolite in the ancient Greek world, ancient Egyptians prised it as the gem of the sun, and historians have speculated that Cleopatra's famous emeralds were olivine rather than beryl.
Hawaii was another historical source, where it was known as Pele's tears. It is now mostly mined out, though the cinder cone called Diamond Head was renowned for its crystals (see our post at http://bit.ly/1zrS1Nz). The grains at the famous Papakolea greensand beach near Hilo (covered at http://bit.ly/2a9hd87) are sand sized peridot crystals.
The most valued colour is a bright olive green, with extra iron content increasing the brown component. The origin of the name is uncertain, but it is one of the birthstones for August, accounting for its continuing popularity.
The main current source remains Arizona, where it occurs as phenocrysts (large crystals that grew slowly before eruption) in a layer of basaltic lava at the top of Peridot Mesa on the San Carlos Apache Reservation. Only inhabitants are allowed to mine it, either in weathered out form gathered in gullies or by drilling and blasting. Other significant sources are Pakistan, China and Burma where it occurs as phenocrysts in basalts or as mantle xenoliths (foreign rocks) carried up by erupting lavas.
There is another amazing source: 4.5 billion year old crystals of peridot from pallassitic meteorites have been occasionally faceted and marketed with this extra cachet. It used to be thought they came from an asteroid's core-mantle boundary, but recent research suggests that they were formed during shattering collisions in the asteroid belt (see our post at http://bit.ly/2aAvdWT)
Loz Image credit: Rob Lavinsky/iRocks.com
http://www.gia.edu/peridot http://webmineral.com/data/Olivine.shtml#.Ug_Xim2O64w http://on.doi.gov/1wVsBW4
Loz
Image credit: Rob Lavinsky/iRocks.com
Papakolea green sand Beach, Mahana Bay, Hawaii.
Green sand beaches are very rare, there are a couple on Hawaii, one on Guam and a third on the Galapagos Island of Floreana. Hawaii's is the greenest, with the densest accumulation of coloured sand. They are volcanic in origin, and the grains consist of olivine phenocrysts eroded out of basaltic volcanics.
The Pu'u Mahana cinder cone erupted 49000 years ago out of Mauna Loa's south-western rift, a magma transport system running down the flank of the mountain. Hawaii's basalts are olivine rich, and this mineral is usually the first to crystallise out of molten magma along Bowen's famous reaction series that established the mineral crystallisation order from magmas. Phenocrysts in basalts are therefore usually olivine and formed in magma chambers or in conduits as the magma rises on its journey to the surface.
As it cools or an eruption occurs, the pressure decreases and crystals start to precipitate. Basalts with visible crystals are called porphyritic and the crystals phenocrysts, while the groundmass of smaller crystalites cooled too rapidly during eruption for large crystals to form. This basalt is very olivine rich, and probably comes from the bottom of a magma chamber, where the mineral settled after precipitating. These late stage eruptions are usually cooler and more viscous, and so produce more explosive pyroclastic deposits rather than lava flows.
The semicircular bay is formed out of the collapsed cinder cone, now breached by the ocean. It was built up of layers of lava, ash and cinder. As the crater walls erode away, the weaker, lighter ash, pyroxene and feldspar are preferentially winnowed out by waves, leaving the tougher denser olivine behind. This constant erosion replenishes 'the beach, but eventually the olivine rich layer will be gone, and the beach will change colour. The bay walls display a record of the eruptions that created the cinder cone.
Gem quality olivine is called peridot, and Hawaii is a traditional source, where it is known as Hawaiian diamond.
Removing the sand is seen as bad luck, potentially bringing Pele's disfavour, which is not something any rockhound or vulcanologist wants.
Loz
Image credit: photorack.net
http://lovingthebigisland.wordpress.com/2009/12/10/bgreen-black-white-grey-and-piebald-the-colored-sand-beaches-of-the-big-island-of-hawaii/
http://www.explore-the-big-island.com/green-sand-beach.html
http://www.sandatlas.org/2012/01/is-papakolea-the-only-green-beach/
http://earthstonestation.wordpress.com/2012/01/28/papakolea-green-sands/
Peridot and ludwigite
Not all the gem olivine out there has its origins in the mantle, some form in high temperature contact metamorphic deposits, when hot olivine rich magmas interact with the country rocks that they intrude. The deep green gemmy specimen in the photo bears a testimony to this origin, in the form of dark needles of the rare magnesium-iron borate mineral Ludwigite. The latter often forms when the magma meets carbonate rocks, producing a diverse metamorphic mineral assemblage known under the umbrella term skarn. Mined in the Maran-Kagan valley of Pakistan, the specimen in the photo measures 3.1 x 2 x .9 cm and has been exhibited in several places as part of the now dispersed Herb Obodda collection.
Our past posts on peridot: http://tinyurl.com/pavuvbq andhttp://tinyurl.com/n9hpgqu.
Loz
Image credit: Rob Lavinsky/iRocks.com
A green beach What you see here is not moss covering Papakōlea beach on the island of Hawai’I, but literally billions of olivine crystals. It is one of four green beaches in the world. The other ones located at Hornindalsvatnet in Norway, Talofofo Beach in Guam and Punta Cormorant on Floreana Island in the Galapagos Islands. So, how did this olivine get there? Papakōlea beach is located in a Bay that is part of a 49,000 year old cinder cone named Pu`u Mahana. This particular cinder cone is composed of olivine-rich magma. Olivine, a silicate mineral made up of iron and magnesium is common in basalt from which it erodes due to its density. Also, olivine is denser than most sand types and thus accumulates on beaches. Eventually the olivine is washed away as well, however, due to erosion the cinder cone keeps a constant supply going. Gem-quality olivine is also known as peridot. The exact origin of the cone is under debate. It was always claimed that Pu`u Mahana is a littoral cone which forms by interaction of the sea and flowing lava. This of course can be very explosive and in combination with wind conditions lava accumulates and a cone is born. However, research has revealed that the cone is over 49,000 years old and calculations of past sea-level revealed that it is practically impossible that this was how the cone was formed (sea level could have been up to 70m lower than today). Thus, the other possibilities could be that Pu’u Mahana is a primary vent, where magma comes to the surface from depth. -OW- Image: www.holestories.com. Papakōlea beach. References: http://hvo.wr.usgs.gov/volcanowatch/archive/2005/05_10_27.html http://geomaps.wr.usgs.gov/parks/coast/sand/gsand2.html
