Fig. 1: Nunderite - an altered volcanic rock

Photo: K. Sieber, www.makrogalerie.de

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There are not only different names and spellings for this rock from Australia in the literature and in the trade, but also different places where it was found. It is questionable whether all these informations mean exactly the same rock. The rock presented to the EPI laboratory with the trade name "Nundorit" consists of light green, cloudy areas embedded in a colorless to brown matrix (Fig. 1). Small particles of opaque ore minerals are unevenly distributed throughout the rock.

Fig. 1: not a "pink larimar", but natrolite

Photo: K. Sieber, www.makrogalerie.de

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At the beginning of 2020, a pink mineral with an attractive texture similar to the pectolite variety "larimar" was found in veins and fissures of a local basalt on the Indonesian island of Nusa Kambangan (Central Java). The stone was promptly marketed under the trade name "pink larimar". Other sources on the Internet state that the zoned mineral aggregates are the mineral thomsonite. The EPI-LAB had the opportunity to examine this gemrock more closely.

Azurite-Gneiss, Pakistan

Foto: K. Sieber, www.makrogalerie.de

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The rock that we are presenting to you looks as if it had been decorated with blue inkblots. It was presented to us as "azurite granite". It is reported that it is found at the foot of the K2 mountain in northern Pakistan. Therefore it is also offered under the trade name "K2".

The structures we saw by using our microscope was similar to that of gneiss. Quartz, biotite and feldspar crystals and a weakly pronounced, layered structure were easily recognizable. In addition, small grains of a green mineral and these strange blue spots are readily visible with the naked eye.

Budstone, South Africa

Foto: K. Sieber, www.makrogalerie.de

The inhomogeneous appearance of a green rock marketed as »Prasem« from South Africa raised doubts about its authenticity. EDX (Energie Dispersive X-Ray) and Raman Laser analyzes performed on some samples confirmed a rock with an inhomogeneous complex mineralogical composition.

Analytical investigations

To our surprise, the X-ray diffraction analysis (EDX) of a sample with particularly hard, dark green to black inclusions reveiled the rare mineral eskolaite together with rutile and chromium bearing mica (fuchsite). Eskolait occurs only at 11 locations worldwide (e.g. Brazil, USA, Russia, India and Finland). Its hardness of 8½ is between spinel and corundum. On the other side the mineral fuchsite has a hardness of only 2½. The resulting differences in hardness within the rock lead to bud-like, roundish weathering forms, which inspired the trade name »Budstone«.

»Dalmatian Stone« is NOT a Jasper

Foto: K. Sieber, www.makrogalerie.de

This speckled rock in black and white, which was named after the Dalmatian dog breed, was long thought to be a porphyrite (a volcanic rock). Also other speculations about the mineralogical composition and formation of this rock, ranging from a volcanic porphyrite to a rock with black tourmaline, were not scientifically proven.

Reason enough for the EPI laboratory to take a closer look at this rock. Even the first analyses of the microstructure led to the assumption that this stone could be a gangue rock. To verify this assumption, it was necessary to precisely determine the mineral composition of this rock. Of particular interest was the way of formation and the nature of the black spots. Therefore we first tried with Raman laser analysis to find out what these black spots consist of. The analyses proved that the black spots cannot be tourmaline, but a mineral from the amphibole group. Since this group is extremely diverse and has numerous solid solution members, no precise conclusions could be optained from the Raman spectrum.

»Dumar«, China

Foto: K. Sieber, www.makrogalerie.de

The origin of the name »Dumar« is unknown. Whether the name has anything to do with the Spanish. Mar = sea is speculative. As origin "China" is indicated.

Like many other newly discovered rocks, »Dumar« was initially called "Jasper" or "Lotusjasper". But the rock has nothing to do with the original jasper. Mineralogical investigations have shown that it's a very complex skarn rock. Skarns are metamorphic rocks formed by metasomatosis from limestone or dolomite rocks.

The Dumar-Skarn consists of a silicified matrix with very fine-grained tremolite, partially intergrown with dolomite and calcite. Additionally radial grown augite and aegirin-augite occur in larger crystals. In the lighter areas they are intergrown with albite feldspar. In between violet domains of fluorite occur, which forms in some regions idiomorphic crystals.

»Eilat Stone«, Israel

Image: K. Sieber, www.makrogalerie.de

From time to time a trade name traditionally used as a quality label is retained, even when the original qualities are no longer available. Often this name is simply transferred to other stones or color varieties that look roughly similar to the original. This is also the case with the so-called »Eilat-Stone«, which appears both on the Internet and on home shopping television.

The classic occurrence of this colorful stone is 25 km north of the city of Eilat, on the southern tip of the State of Israel. In the Timna valley, on the edge of the Negev desert, copper ore was mined over 5000 years ago. The legendary copper mines of King Solomon, from which most of the turquoise used in ancient Egypt originate, are located in the same area.

»Eilat-Stone« is composed of a variety of copper minerals, especially carbonate minerals (malachite, azurite), phosphate minerals (pseudomalachite, turquoise) and silicates (chrysocolla, quartz). Depending on how these components are distributed, blue, blue-green or green colors dominate. These copper mineralizations are formed in a magmatic complex of predominantly granitic composition, which is about 550 million years old. The magmatic activity produced copper-bearing solutions from which copper minerals crystallized, leading to complex mineral aggregations in the oxidation zone.

finely dispersed fluorite gives this Fluorite-Opal-Jasper (»Tiffany Stone«) it's purple color

Foto: K. Sieber, www.makrogalerie.de

At the beginning of the millenium many tumbled stones we sold under the trade names »Tiffany Stone« and "Fluorite Opal".

This beige rock with violet veins, which is known in the USA as "Tiffany Stone" is provided by a large number of small deposits in southwestern Utha (USA), which came to be known as "Spore Mountain Lavender Mines". In Europe tumbled stones were sold under the name "Fluorite Opal".

The rock owes its formation to the activity of volcanoes, which deposited in several eruptions large quantities of silica-rich ash layers in an area dominated by limestones. Between the sporadic eruptions quartz-rich sediments were gradually solidified and transformed. Fluorine-containing gases led to an impregnation of the sediments with fluorite. In an older period mainly quartz, quartzite, jasper, agate and flint were formed along the contact to the underlying limestone. Manganese ores associated with the limestone, were incorporated and form brown to black, often metallically shiny veins in the rock.

»Lavender-Jade« (Jadeite - Metagranitoide), Turkey

Foto: K. Sieber, www.makrogalerie.de

The world-famous deposit for this lilac-colored rock is located near Harmancik, about 90 km south of Bursa in Turkey. The deposit covers an approx. 400m thick jadeite-bearing metamorphous rock embedded between mica schists and marbles. It was formed about 80 million years ago from an originally granitic rock (granitoid) by high-pressure metamorphism. The resulting metagranitoid rock consists of quartz, chlororitoid, lawsonite, glaucophane and phengite as well as up to 50% jadeite.

Jadeite occurs in this rock not only in the violet color of »Lavender Jade«. To a small extent you can find it there also in grey, white and green. The violet color variety developed during the metamorphosis process by the circulation of manganese-containing aqueous solutions.

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»Llanite Rhyolite«, Madagaskar

Foto: K. Sieber, www.makrogalerie.de

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A colorful rock with roundish to oval domains of shimmering bluish colors, is marketed as »Llanite«, »Llianit« or »Llanoithe« or simply as "Porphyrite" and "Volcanite". The latter term gives an idea about its formation ("it is from volcanic origin") but it does not specify what kind of rock it is - there are many different volcanic rocks out there. The term "Porphyrite" is an outdated name for a class of volcanic rocks, called "rhyolite" in modern time. The term »Llanite« is based on the place of discovery in Llano County, Texas, USA. Known occurrences of rhyolithic rocks with this specific look are Brazil, Madagascar and the USA.

The samples we have examined in the EPI-Lab, were reported to come from Madagascar. We identified a slightly metamorphosed (alkalifeldspar-) rhyolite with exceptionally large crystals, embedded in a fine grained groundmass. Orthoclase feldspar crystals up to 10mm / 0.4in in size and large quartz and plagioclase feldspar crystals up to 5mm / 0.2in are visible to the naked eye. The analyses of various thin sections revealed a well crystallized groundmass. It consists of quartz, mica and feldspar very rich in inclusions, with no glassy component.

Mariposite-Dolomite

Foto: K. Sieber, www.makrogalerie.de

»Mariposite dolomite« is a white stone with green striationss. It occurs in different places in the Sierra Nevada in California (USA), for example around Coulterville in Mariposa County. Benjamin Silliman Jr. named the stone after this region in 1868. Its occurrence is linked to a contact zone of argillaceous schists and ultrabasic rocks.  Therefore dolomite and quartz coexist together with green phyllosilicates. These silicates are in a large part mariposite (a chrome-muscovite mica) but sometimes also of nickeliferous chlorite.

Minerals of the mica group are classified in white micas and dark micas depending on their appearance. Muscovite is a common member of the white mica group. The pure mineral is colorless and transparent. Variations in its chemical composition modify its physical properties (e.g. flexibility, color). Such varieties bear their own names like »Fuchsite« for a chrome mica or »Phengite« for SiO₂ rich mica and »Mariposite« which is rich in chrome and SiO₂. Sometimes Mariposite is also called »Chromium phengite« because of it's high content of chrome and SiO₂.

The macro photography (size 3 x 4 cm) of Maw-Sit-Sit shows the finely matted structure of this jadeite-containing rock.

Foto: K. Sieber, www.makrogalerie.de

Maw-sit-site is a rock that consists of six main components that can vary significantly in quantity. The appearance of individual specimens can vary noticeably. This name is derived from a local name of its provenance near the town of Tawmaw in Burma (Myanmar) [Gübelin, 1978].

The rock consists of a groundmass of light-colored aggregates (mainly albite, but also zeolites and chlorite) in composition with numerous dark minerals, especially minerals of the jadeite-cosmochlor solid solution series of intense green color. These jadeite minerals can form single crystals or a blocky mosaic. In between, there are always black nests of fine felted cosmochlore (NaCrSi₂0₆), a chromium analogue of jadeite (NaAlSi₂0₆).

Due to the replacement of Al by Cr, maw-sit-sit contains wide sequences of a solid solution between cosmochlore and jadeite. In the centre of the cosmochlore nests metallically shiny chromite can be found in form of small residual grains. In addition, coarser crystals of grey to green colored amphibole or chrome-amphibole were formed. In the sixties and seventies of the last century this rock was also called "Jadealbit". However, since maw-sit-sit has been increasingly offered, hardly any albite can be found. As a consequence this appellation is considered obsolete.

Piemontite Quartzite rock, Norway

Image: K. Sieber, www.makrogalerie.de

The best known deposit of »Thulite«, the pink variety of the mineral Zoisite, lies in Norway in the region of Lom. Lom is also the location of piemontite-quartzite which looks very similar to »Thulite« and can easily be mistaken for it.

»Thulite« and Piemontite are Calcium Aluminium Silicates with the same chemical formula Ca₂Al₃(SiO₄)₃(OH) (+ Mn, Fe), which crystallize in different crystal systems: »Thulite« (zoisite) in the orthorhombic crystal system, piemontite (klinozoisite) in the monoclin crystal system. When aluminium (Al) is substituted by manganese (Mn), both modifications show pale reddish to strong pink colors. 

The deposit is located in a zone of gneisses of sedimentary origin (paragneisses) of the so-called "Western Gneiss Region", in which numerous inhomogeneities such as quartz lenses and amphibolites occur. Embedded in this is a layer of about 3 x 250 m of manganese-rich minerals such as piemontite and thulite, with varying proportions of quartz, muscovite mica, tremolite and calcite.

Fig. 1: »Pinolite« - The resemblance to pine nuts gave this magnesite rock its name.

Photo: K. Sieber, www.makrogalerie.de

The Sunk/Hohentauern deposit in Styria (Austria) is known worldwide for a rock forming magnesite with a typical coarsely crystalline growth structure which resemble pine nuts or ice flowers in shape. Because of this special texture the rock was named »Pinolite« (pignolia = pine nut) or "ice flower magnesite". Large, bright magnesite crystals are embedded in a gray, fine-grained matrix rich in inorganic pigment.

Until 1963 the rock was mined as decorative rock and marketed under the name "Sunk" (the name of the finding place). Today it is found almost exclusively in arts and crafts objects or as tumbled stones.

»Rainbow Basalt«, USA

Foto: K. Sieber, www.makrogalerie.de

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A dark basalt from Michigan (USA) with roundish cavities, filled with colorful minerals has been given the trade name »Rainbow Basalt«.

Basaltic rocks are formed wherever thin, low-silica magma emerges at the earth's surface in volcanically active zones and cools down relatively quickly to basalt lava. Beside very fine-grained plagioclase feldspars and pyroxene minerals, olivine and magnetite may also be present, as well as an uncrystallized glassy component. Sometimes basalt lavas are  quite rich in gaseous components. Therefore roundish cavities are frequently found.

Shattuckite-Chrysocolla-Quartz, Kongo

Foto: K. Sieber, www.makrogalerie.de

The copper deposit Tantara in Congo is known for its very nice specimens of plancheite and shattuckite with dioptase and white calcite. It also provides a rock composed of Shattuckite, Quartz, Chrysocolla, Azurite, Malachite, Bornite and other copper ores, sold simply as "Shattuckite".

The dark blue copper mineral shattuckite usually occurs as needles or fibrous crystals in radiating or massive mineral aggregats. It is formed as a secondary mineralization in the oxidation zone of copper deposits. With a Mohs hardness of 3½ it is too soft for jewelry.

However, embedded in quartz and together with other copper minerals like azure chrysocolla and/or grass-green malachite it makes up a mineral composition that takes a good polish and is not only pleasant to look at but also an attractive collector's stone.

Sodalite-Syenite, Brasil

Image: K. Sieber, www.makrogalerie.de

This blue and white speckled stone, which is very popular as a gemrock, has been mined in Brazil since 1965. The name "Azul Bahia", which is commonly used in the stonemasonry industry, refers to this origin.

Petrologically, it is a syenite rock with approx. 50% microclinic feldspar, 30% sodalite, 10% cancrinite, 5% plagioclase as well as 5% aegirine and other dark components. Syenites are magmatic alkaline rocks with a very low content of quartz, but often enriched with exotic minerals. Their main mineral composition usually comprises alkali feldspars, amphibole- and/or pyroxenes-minerals or plagioclase feldspars and biotite. In addition, rare minerals such as astrophyllite, eudialyte or (as in in the case of sodalite syenite) sodalite occur in larger quantities.

»Sonora Sunrise«, Mexico

Foto: K. Sieber, www.makrogalerie.de

This colorful stone comes from the Milpillas Copper Mine west of the small town Cananea in the North Mexican Sonoran Desert. The mine is small and produces not very much material. As a consequence the stones achieve high prices ever since their market launch in 2006.

Depending on the mineral composition the color varies from brownish red with olive-green spots, to black areas with a metallic luster, together with blue and green areas, grown closely together like a patchwork. Using X-ray diffraction analysis (EDX) the green-blue zones could be identified as an intergrowth of  brochantit (a copper sulfide) with the green copper silicate chrysocolla. The brownish to orange-red areas consist of the copper oxide cuprite grown together with another copper oxide: tenorite.