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Cinnabar       

HgS

Locality:

Siele Mine, Piancastagnaio, Siena Province, Tuscany, Italy

Field of view: 3mm

Largest crystal size: 1mm

Aggregate of red cinnabar crystals, of unusual habit. The 1 mm measurement refers to the height of the major crystal on the right.

Collection and photo of Gianfranco Ciccolini.

Cinnabar generally occurs as a vein-filling mineral associated with recent volcanic activity, alkaline hot springs, low-temperature hydrothermal, in veins and sedimentary, igneous, and metamorphic host rocks.. The mineral resembles quartz in symmetry and in its exhibiting birefringence. Some cinnabar that contains trace amounts of chlorine will darken with exposure to sunlight. Principal ore of mercury. Used as a cosmetic pigment in ancient times.

Be aware that cinnabar from some localities, especially samples which are 'massive' rather than crystalline, may contain traces of native mercury, and this is far more easily absorbed by the body.

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Bariopharmacosiderite    

Ba0.5Fe3+4(AsO4)3(OH)4·5H2O

Locality:

Clara Mine, Oberwolfach, Ortenaukreis, Freiburg Region, Baden-Württemberg, Germany

Field of view: 2.09 mm

Collection: Heinz Förch Photo: Michael Förch

Bariopharmacosiderite is a rather rarely occurring mineral from the mineral class of the “ phosphates , arsenates and vanadates ”. A secondary mineral coating fractures and cavities in tetrahedrite-tennantite bearing rocks undergoing near-surface weathering. Easily soluble in warm hydrochloric acid.

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Acanthite              

Ag2S

Locality:

Mascot Mine (Gorham Lead mine; Galena King mine), Gorham, Coos Co., New Hampshire, USA

Largest crystal 0.5 mm

Tom Mortimer's Photo

Acanthite is a form of silver sulfide a common silver mineral in moderately low-temperature hydrothermal veins and in zones of supergene enrichment. Typically found as pseudo-cubic and pseudo-octahedral crystals, paramorphic after argentite.

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Almandine              

Fe2+3Al2(SiO4)3

Locality:

Mesolcina Valley (Misox), Grisons, Switzerland

Field of view: 5mm

Almandine crystal with a strong spessartine component (Fe:Mn ~= 3:2) in mica (probable muscovite) found in a pegmatitic environment.

Photo Mischa Crumbach and collection Philippe Roth

Almandine A species of mineral belonging to the Garnet group. The name derived from the town Alabanda, Caria in Asia Minor. Almandine is an iron alumina Garnet, of deep red color, inclining to purple. The most common garnet, typically in mica schists and gneisses, from regionally metamorphosed argillaceous sediments and pelites; also in contact metamorphic hornfels. In granites and eclogites; in sedimentary rocks; as a detrital mineral.

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Safflorite, Skutterudite              

Safflorite : (Co,Ni,Fe)As2

Skutterudite : CoAs3

Locality:

Sophia Mine, Böckelsbach valley, Wittichen, Schenkenzell, Rottweil, Freiburg Region, Baden-Württemberg, Germany

Field of view: 2.5 mm

Safflorite twins in iridescent colours with silver grey and blocky skutterudite.

Collection and photo: Stephan Wolfsried

Safflorite is a rare cobalt iron arsenide mineral. In hydrothermal veins of moderate temperature and pressure.

Skutterudite is a cobalt arsenide mineral containing variable amounts of nickel and iron substituting for cobalt. Materials with a skutterudite structure are studied as a low cost thermoelectric material with low thermal conductivity. Typically in medium- to high-temperature hydrothermal veins with other Ni–Co sulfide minerals.

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Uvarovite, Amesite              

Uvarovite : Ca3Cr2(SiO4)3

Amesite : Mg2Al(AlSiO5)(OH)4

Locality:

Saranovskii Mine ("Rudnaya" underground chromite mine; Glavnoe Saranovskoe deposit), Saranovskaya Village (Sarany), Gornozavodskii District, Perm Krai, Russia

Field of view: 2.5 mm

Tiny dodecahrons of uvarovite on elongated and stacked appearing crystals of amesite.

Collection K. Pirabee, photo Martin Reich

Uvarovite is one of the rarest of the garnet group minerals, and is the only consistently green garnet species, with a beautiful emerald-green color. It occurs as well-formed fine-sized crystals. Hydrothermal alteration of chromite-bearing serpentinite, metamorphosed limestones, and skarns.

Amesite is an uncommon silicate mineral of Kaolinite-serpentine group that forms in low grade metamorphism of Al-, Mg-rich rocks.

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Delafossite              

CuFeO2

Locality:

Gosenbach, Siegen, Siegen-Wittgenstein, Arnsberg, North Rhine-Westphalia, Germany

Delafossite on limonite. Field of view 5.5 mm.

Matthias Reinhardt’s Photo 

Delafossite is a copper iron oxide mineral with formula CuFeO2 or Cu1+Fe3+O2. It is a member of the delafossite mineral group, which has the general formula ABO2, a group characterized by sheets of linearly coordinated A cations stacked between edge-shared octahedral layers (BO6). Delafossite, along with other minerals of the ABO2 group, is known for its wide range of electrical properties, its conductivity varying from insulating to metallic. Delafossite is usually a secondary mineral that crystallizes in association with oxidized copper and rarely occurs as a primary mineral. Weakly magnetic

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Mimetite

Pb5(AsO4)3Cl

Locality:

Rouez mine, Sarthe, Pays de la Loire, France

1.14 mm group of Mimetite crystals.

Collection & photo Matteo Chinellato

It is a secondary mineral found in the oxidized zones of lead mineral deposits, and in other settings where lead and arsenic occur together. Piezoelectric. Soluble in HNO3 and KOH. Forms pseudomorphs after an unknown mineral (possibly Anglesite ). Industrially, mimetite is a minor ore of lead. The chief use of mimetite is as a collector's specimen, often creating attractive botryoidal crusts on the surface of the specimen. Though mimetite is also found in prismatic crystal forms, it is not used as a gemstone due to its softness (3.5 - 4).

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Pseudomalachite

Cu5(PO4)2(OH)4

Locality:

Silberbrünnle Mine, Haigerach valley, Gengenbach, Ortenaukreis, Freiburg Region, Baden-Württemberg, Germany

Field of view: 0.65mm

Collection and photo: G. Franz Zöll

A secondary mineral in the oxidized zone of hydrothermal copper deposits. Soluble in acids. Crystals, which are rare, are prismatic, usually with uneven faces. Pseudomalachite is commonly compact, reniform or botryoidal, or it may be fibrous or in crusts and films.

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Cassiterite, Rhodizite   

Cassiterite : SnO2

Rhodizite : (K,Cs)Al4Be4(B,Be)12O28

Locality:

Ampasogona pegmatite, Tetezantsio-Andoabatokely Pegmatite Field, Andrembesoa, Betafo, Vakinankaratra, Madagascar 

7 mm group of rare combination of Rubidium-rich Rhodizite with Cassiterite on feldspars.

Collection Natural History Museum of Milan #38940 photo Matteo Chinellato

Cassiterite is the primary ore of Tin, this mineral is found in hydrothermal veins and pegmatites associated with granite intrusions. Because of its durability, it is also frequently found concentrated in alluvial placer deposits, sometimes in large enough quantities to be commercially exploitable. Isostructural with Rutile.

Rhodizite is a rare late-stage accessory mineral in alkali-rich granite pegmatites. Rhodizite is named from Greek "rhodizein" - rose-coloured, alluding to the red tinges it gives in a blowpipe flame. Rhodizite is found as well-formed transparent to translucent colourless to white, sometomes pink, red, yellow-green, yellow, grey crystals. Rhodizite has a high lustre and hardness, but it is very rare and crystals are usually too small to facet. Faceted stones exceeding 1 carat are uncommon.  Pyroelectric.

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Prehnite             

Ca2Al2Si3O10(OH)2

Locality:

Oficarsa Quarry (Cerro de las Culebras), Carchelejo, Cárcheles, Jaén, Andalusia, Spain

Largest crystal size: 13 mm

Crystals of prehnite, arranged in a fan, light green.

Collection and photo of Gianfranco Ciccolini.

Prehnite is a secondary or hydrothermal mineral in veins and cavities in ma¯c volcanic rocks; less commonly in granite gneiss or syenite; a typical product of low-grade metamorphism. Extensive deposits of gem-quality prehnite occur in the basalt tableland surrounding Wave Hill Station in the central Northern Territory, of Australia.

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Marcasite, Pyrite, Dolomite

Marcasite: FeS2

Pyrite: FeS2

Dolomite: CaMg(CO3)2

Locality:

Beez, Namur, Namur, Wallonia, Belgium

Field of view 2 mm

Marcasite crystals grown around a pyrite cubo-octahedron, on dolomite.

Photo & collection Chollet Pascal

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Clinochlore (Var: Chromian Clinochlore), Hydromagnesite    

Clinochlore (Var: Chromian Clinochlore) : Mg5(Al,Cr)2Si3O10(OH)8

Hydromagnesite: Mg5(CO3)4(OH)2·4H2O

Locality:

Kop Krom mine, Kop Daglari, Aşkale District, Erzurum Province, Turkey

Largest crystal size: 4 mm

Stefan Koch's Photo

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Covellite

Covellite : CuS

Locality:

Madielle quarries, Madielle quarrying basin, Massa, Massa-Carrara Province, Tuscany, Italy

Blue covellite blades of 0.5 mm on calcite.

Collection & Photo: Matteo Chinellato

Covellite (also known as covelline) is a rare copper sulfide mineral with the formula. This indigo blue mineral is commonly a secondary mineral in limited abundance and although it is not an important ore of copper itself, it is well known to mineral collectors. The mineral is generally found in zones of secondary enrichment (supergene) of copper sulfide deposits. Research of its unique properties has only surged in past decade yet promising results suggest may be used widescale in certain specific applications in the future.

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Diaspore, Natrolite      

Diaspore : AlO(OH)

Natrolite : Na2Al2Si3O10·2H2O

Locality:

Saga 1 Quarry, Sagåsen, Auenslandet, Porsgrunn, Telemark, Norway

Field of view: 2.74 mm

Zoned, platy, twinned diaspore crystals with clear, prismatic natrolite crystals from the Saga Quarry. The specimen was collected by Svein Arne Berge.

Photo by OT. Ljøstad

Diaspore, also known as diasporite, empholite, kayserite, or tanatarite, is an aluminium oxide hydroxide mineral, crystallizing in the orthorhombic system and isomorphous with goethite. It occurs sometimes as flattened crystals, but usually as lamellar or scaly masses, the flattened surface being a direction of perfect cleavage on which the lustre is markedly pearly in character. It is colorless or greyish-white, yellowish, sometimes violet in color, and varies from translucent to transparent.

Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate.

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Pyromorphite, Quartz

Pyromorphite : Pb5(PO4)3Cl

Quartz : SiO2

Locality:

Bwlch Glas Mine, Talybont, Ceulanymaesmawr, Ceredigion, Wales, UK

Field of view: 10 mm

Pyromorphite on Quartz.

Collection and Photo: Louis Verschuren

Pyromorphite is a mineral species composed of lead chlorophosphate sometimes occurring in sufficient abundance to be mined as an ore of lead. Crystals are common, and have the form of a hexagonal prism terminated by the basal planes, sometimes combined with narrow faces of a hexagonal pyramid. Crystals with a barrel-like curvature are not uncommon.Piezoelectric if biaxial. Soluble in HNO3 and KOH. Slightly soluble in carbonated water. Forms pseudomorphs after Galena and Cerussite (common). Galena frequently occurs as more or less complete pseudomorphs after pyromorphite. Other pseudomorphs include Apatite after Pyromorphite and Plumbogummite encrusted on, and replacing, Pyromorphite. May be yellow to orange in SW and LW UV light

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Azurite, Agardite              

Azurite : Cu3(CO3)2(OH)2

Agardite general chemical formula: (REE,Ca)Cu6(AsO4)3(OH)6·3H2O

Locality:

Clara Mine, Oberwolfach, Ortenaukreis, Freiburg Region, Baden-Württemberg, Germany

Field of view: 2.15mm

Collection and photo: G. Franz Zöll

Agardite is a mineral group consisting of agardite-(Y), agardite-(Ce), agardite-(Nd), and agardite-(La). They comprise a group of minerals that are hydrous hydrated arsenates of rare-earth elements (REE) and copper. They form needle-like yellow-green crystals in the hexagonal crystal system.