On the grounds of the de Beer's "Big Hole" museum at the former diamond mine in Kimberly, South Africa.
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This is Rhodochrosite from the N'Chwaning Mine, Kuruaman Field, Kalahari, Northern Cape, South Africa at the Tucson Gem & Mineral Show.
en.wikipedia.org/wiki/Rhodochrosite
Rhodochrosite occurs as a hydrothermal vein mineral along with other manganese minerals in low temperature ore deposits as in the silver mines of Romania where it was first found. Banded rhodochrosite is mined in Capillitas, Argentina.
It was first described in 1813 in reference to a sample from Cavnic, Maramureş, present-day Romania. The name is derived from the combination of Greek words ροδόν (rodon, meaning rose) and χρωσις (chrosis, meaning coloring).[2]
Rhodochrosite is mainly used as an ore of manganese, which is a key component of low-cost stainless steel formulations, many tool steels, and certain aluminium alloys.[9] Quality banded specimens are often used for decorative stones and jewellery. Due to its softness and perfect cleavage it is rarely found faceted in jewellery and is also sought after by many collectors.[10]
fineart.ha.com/itm/minerals/cabinet-specimens/rhodochrosi...
Rhodochrosite
N'Chwaning I Mine, N'Chwaning Mines, Joe Morolong Local Municipality, John Taolo Gaetsewe District Municipality, Northern Cape, South Africa
For so many mineral collectors, the Rhodochrosites of the N'Chwaning I Mine have become the holy grail of collecting, more so due to their increasing scarcity on the modern market,
www.mindat.org/loc-55925.html
The N'Chwaning mines term is used to group together three manganese mines located in the Northern Cape Province of South Africa. These mines (or shafts) are known as N'Chwaning I (est. 1972), N'Chwaning II (production started in 1981) and N'Chwaning III (became fully operational in 2006).
The N'Chwaning mines comprise one of the largest manganese reserves in South Africa, having estimated reserves of 323.2 million tonnes of manganese ore grading 42.5% manganese.
Apart from their ore producing significance, the N'Chwaning mines are notable and famous among the mineral collecting community for producing high-quality mineral specimens of rhodochrosite, manganite, ettringite, inesite, jouravskite and other minerals. The majority of the major mineral finds documented originate from the N'Chwaning II shaft.
Geology: The manganese ores of the Kalahari Manganese Field are contained within sediments of the Hotazel Formation of the Griqualand West Sequence, a subdivision of the Proterozoic Transvaal Supergroup. The N'Chwaning deposit consists of a gently dipping and regular strata bound body of high-grade ore, which has undergone a hydrothermal upgrading associated with faulting.
The base of the Hotazel Formation consists of a bright-red banded iron-formation bed (varying from massive to fine-grained specularite and/or euhedral magnetite crystals) overlying volcanic glass breccias and lavas of the Ongeluk Formation. The banded iron-formation units grade into microcrystalline kutnohoritic ovoid-rich braunite rock. The kutnohorite in this area is concentrated in ovoids, which represent partially compacted, early diagenetic concretions in hematite and braunite rock. The braunite rock bed of the lower section of the lowest of the three sedimentary cycles present in the Hotazel Formation is between 5 and 45 m thick. This is the major ore unit of the Kalahari manganese field, with a manganese content varying between 20 and 48 weight percent. The middle manganese-bearing unit (cycle 2) is a maximum of 2 m thick and is not economically viable. The top manganese orebody was mined in previous years. It rarely exceeds 5m thickness. Grey hematitic and manganese minnesotaite rocks are found between the lower and the middle manganese orebodies.
About 1300 million years ago a widespread hydrothermal event occurred in the north-western portion of the Kalahari manganese field which reached temperatures up to 450 °C in the Wessels, N'Chwaning and Black Rock Mines. This event decarbonated and desilicated portions of the Hotazel Formation to the north-west and thus upgraded the manganese content of the ore. Furthermore, the hydrothermal event is of great significance from the collectors' point of view, as a wide range of rare as well as unusual mineral combinations were produced.
The manganese orebodies in the north-western part of the Kalahari manganese field (Wessels, Black Rock, and N'Chwaning Mines) have been termed Wessels-type ore. These orebodies contrast markedly to the primary Mamatwan-type ore. The ore has been hydrothermally altered and metamorphosed. This resulted in a manganese ore with a coarser grain size with higher manganese content. This ore is braunite-rich and contains other major minerals such as braunite II, bixbyite, hausmannite, marokite, and hematite together with minor amounts of calcite. The overall carbonate content of the Wessels-type ore is lower than that of the Mamatwan-type ore. Andradite and barite are common gangue minerals. Additionally, minor minerals such as tephroite and rhodochrosite as well as aegirine (in the iron formation above the ore layers)are associated with this ore type. Most of the Wessels, Black Rock, N'Chwaning II and parts of N'Chwaning I ores are of this type.
www.visittucson.org/tucson-gem-mineral-fossil-showcase/
"Every year the world-renowned Tucson Gem, Mineral & Fossil Showcase is like a time portal, a trip around the world, and a treasure hunt all rolled into one. Every winter, more than 65,000 guests from around the globe descend upon Tucson, AZ, to buy, sell, trade, and bear witness to rare and enchanting gems, minerals, and fossils at more than 50 gem show locations across the city. If you're planning a winter visit to Tucson, you won't want to miss this three-week-long event filled with shows, related events, a free day at the gem & mineral museum, and much, much more!
"Whether you’re looking for a $5 shimmering crystal necklace or a show-stopping $200,000 crystallized rock from an exotic location, the Tucson Gem, Mineral, & Fossil Shows have something for everyone."
www.visittucson.org/blog/post/gems-and-minerals/
www.tgms.org/show
The theme this year was Shades of Green- Experience the Magic. The theme for next year's show will be Red, White, and Blue Celebrate the Spirit of Minerals
xpopress.com/news/article/783/shades-of-green-70th-annual...
TGMS 2025
Tucson Gem Show 2025