Metamorphic Minerals

• Actinolite
• Alurgite
• Andalusite
• Andalusite (chiastolite)
• Antigorite
• Anthophyllite-Gedrite
• Biotite
• Brucite
• Calcite
• Cassiterite
• Charoite
• Chlorite
• Chloritoid
• Chrysocolla
• Cordierite
• Corundum
• Corundum (ruby)
• Kyanite
• Kornerupine
• Kyanite (reticite)
• Deerite
• Dumortierite
• Epidotes
Allanite
Pistacite
Piemontite
Zoisite

• Fassaite
• Fluorite
• Glaucophane
• Garnet
• Hercynite
• Hedenbergite
• Hydrogrossular
• Howieite
• Humites
• Jadeite
• Lawsonite
• Lazulite
• Lazurite
• Malachite
• Minnesotaite
• Muscovite
• Olivine
• Omphacite
• Omphacite Cr
• Pargasite
• Piemontite (Praborna)
• Pyrite
• Prehnite
• Pumpellyite
• Quartz
• Rhodonite
• Rutile
• Sapphirine
• Scapolite
• Serpentine
• Sillimanite
• Sillimanite (fibrolite)
• Staurolite
• Stilpnomelane
• Sugilite
• Talc
• Taramellite
• Thulite
• Tinaksite
• Tinzenite
• Titanite
• Tremolite
• Tourmaline
• Vesuvianite
• Violan
• Wollastonite
• Yoderite
• Zussmanite

Texture and Microstructure

• Augen
• Book shelf sliding
• Boudinage
• Corona
• Decussate
• Deformation lamellae
• Deformation twins
• Crenulation cleavage
• Fringes
• Granoblastic
• Kelyphite
• Kink Bands
• Lepidoblastic
• Mesh
• Mica fish
• Mylonitic
• Nematoblastic
• Oblique foliations
• Polygonal
• Porphyroblastic
• Porphyroclastic
• Pseudomorph
• Ribbon
• S-C fabric
• Skeletal garnet
• Symplectite
• Veins

Metamorphic Rocks

• Albite greenshist
• Amphibolite (felsic)
• Amphibolite (mafic)
• Amphibolite (mylonitic)
• Amphibolite with epidote
• Andalusite schist
• Anyolite
• Augen gneiss
• Blueschist
• Blueschist (Ile de Groix)
• Blueschist (retrograde)
• Buchite
• Calc-schists
• Carbonated peridotite
• Cataclasite
• Charoitite
• Chlorite schist
• Chloritoid Schist (Ile de Groix)
• Cordierite slate
• Corundum-fuchsite rock
• Deformed oolite
• Dunite (mylonitic)
• Eclogite
• Eclogite Porto Ottiolu
• Epidosite
• Gabbro (mylonitic)
• Garnet micaschist
• Glaucophane granofels
• Granite (mylonitic)
• Granulite (felsic)
• Granulite (mafic)
• Granulite (retrograde)
• Granulite (sapphirine-bearing)
• Greenschist
• Hornfels
• Hornfels (albite-epidote)
• Hornfels (cordierite, plagioclase)
• Hornfels (corundum, plagioclase)
• Hornfels (hydrogarnet)
• Jadeite metagranite
• Jadeitite
• Kinzigite
• Lapis lazuli
• Marble
• Marble (calc-silicate)
• Marble (diopside)
• Marble (forsterite)
• Marble (mylonitic)
• Marble (tremolite)
• Mylonite
• Ocean jasper
• Ophicalcite
• Peridotite (mylonitic)
• Phyllite
• Prasinite
• Pseudotachylyte
• Pseudotachylyte (Ivrea-Verbano)
• Quartzite
• Quartzite (tourmaline)
• Rhyolite (mylonitic)
• Rodingite
• Schist
• Seafloor basalt
• Serpentinite
• Serpentinized lherzolite
• Skarn
• Skiddaw Metamorphic Aureole
Skiddaw
1) Spotted slate
2) Andalusite slate
3) Cordierite slate

• Slate
• Slate (ottrelite)
• Talc schist
• Tourmalinite
• Ultramylonite (granitic)
• Ultramylonite (mafic)

Sassi Neri Skarn (Pargasite-Skarn)

Skarn is an old Swedish mining term originally used to describe a type of silicate gangue, or waste rock, associated with iron-ore bearing sulfide deposits apparently replacing Palaeoproterozoic age limestones in Sweden's Persberg mining district. In modern usage the term "skarn" has been expanded to refer to calcium-bearing silicates of any age. In America the term "tactite" is often used synonymously with skarn.

Skarn is a relatively simple rock type defined by its mineralogy and usually is dominated by calc-silicate minerals, such as garnet and pyroxene. Skarns are present on all continents and in rocks of almost all ages. Although the majority of skarns are found in lithologies containing at least some limestone, they can form in almost any rock type, including shale, sandstone, granite, iron formation, basalt, and komatiite. Skarns can form during regional or contact metamorphism and from a variety of metasomatic processes involving fluids of magmatic, metamorphic, meteoric, and/or marine origin. Although most are found adjacent to plutons, they also can occur along faults and major shear zones, in shallow geothermal systems, on the sea floor, and at lower crustal depths in deeply buried metamorphic terranes. In addition to this geologic variability, skarns have been mined for a variety of metals, including Fe, W, Cu, Pb, Zn, Mo, Ag, Au, U, rare earth elements (REE), F, B, and Sn.

Skarns can be subdivided according to several criteria. Exoskarn and endoskarn are common terms used to indicate a sedimentary or igneous protolith, respectively. Exoskarn and endoskarn also can refer to the location of skarn relative to the causative pluton (external versus internal), although such a distinction is not meaningful when multiple plutons or no igneous rocks are present. Magnesian, mangan, and calcic skarn can be used to describe the dominant composition of the protolith and resulting skarn minerals. Such terms can be combined, as in the case of a magnesian exoskarn, which contains forsterite-diopside-phlogopite skarn formed from dolostone.

Skarnoid is a descriptive term for calc-silicate rocks which are relatively fine grained, Fe poor, and which reflect, at least in part, the compositional control of the protolith. Genetically, skarnoid is intermediate between a purely metamorphic hornfels and a purely metasomatic, coarse-grained skarn. Due to typical compositions of sedimentary protoliths it generally is pale in color and Fe poor in composition.

For all of the preceding terms, the composition and texture of the protolith tend to control the composition and texture of the resulting skarn. In contrast, most economically important skarn deposits result from large-scale metasomatic transfer, where fluid composition and infiltration pathways control the resulting skarn and ore mineralogy. Even though many of these terms are fairly specific, there is a continuum, both conceptually and in the field, between purely metamorphic and purely metasomatic processes.

Importance of Skarn deposits:

1. They are important sources of Fe, Cu, Zn, W, Mo and other metals, as well as of the industrial minerals asbestos, magnesite, talc and wollastonite.
2. They are closely associated genetically and spatially with intrusive igneous rocks.
3. They are closely associated genetically and spatially with other types of ore deposits, such as porphyry copper and greisen deposits.
4. Their intimate admixture of iron-rich skarn minerals and ore minerals implies that skarns may provide natural examples of the laboratory processes of sulfidation and oxidation.
5. They are essentially retrogressive; that is, they form with falling temperature. This feature promotes the formation of mineral assemblages of low variance. Several facies or phases of skarn formation can be studied in a single hand specimen or thin section.
6. They are generally coarse-grained and the minerals are strongly colored. This features is convenient for the study of textures and zoning in hand specimen.

How may skarn be distinguished from mineralogically similar rock types such as calc-silicate hornfels? In the first place, as recognized by Goldschmidt (1911), skarns tend to be distinctly more coarse-grained than hornfelses. Skarn garnets commonly exceed 2-3 cm in diameter, and clinopyroxene crystals are 10 cm or more long. This coarse grain size is presumably indicative of crystal growth from high temperature, mineral-rich fluids (like the giant crystals in pegmatites ).

A second characteristic is that skarns consist of minerals with distinctive colors (especially, weathering colors) and chemistry. The garnets in skarn tend to be andradite rather than grossular, and the clinopyroxenes hedenbergite or johannsenite rather than diopside. This enrichment in Fe and Mn generally causes skarns to be dark-weathering. Enrichment in pneumatolytic elements, such as B (in axinite, datolite and other borosilicates and borates) and F (in Auorite, apophyllite, humite-group minerals, micas and amphiboles), is also common.
Thirdly and most distinctively, skarns tend to be metasomatically zoned around the presumed passageways of hydrothermal fluids - igneous contacts, sedimentary contacts, faults and fissures. In hornfelses, in contrast, the calc-silicate distribution is strictly controlled by bedding and by original chemical inhomogeneities in the rock.

An indication of metasomatic zoning in skarns is that skarns typically consist of a sequence of more-Or-Iess monomincralic bands that replace each other across sharp boundaries. This original zoning may be partly obscured by cross-cutting late hydrothermal alterations, but it is still generally recognizable. The abundance of late hydrothermal alteration is itself a distinctive feature of skarns as contrasted with hornfelses. Lastly, an obvious distinctive feature of skarns is their association with the mineable ores contained within them.

The formation of skarn deposit

The formation of a typical skarn deposit seems to involve a number of stages, as revealed by textural and spatial relations among the minerals.

1. Intrusion of an intermediate to granitic magma occurs at 900-700° C, probably at shallow depths (perhaps ranging from tens or hundreds of meters to several kilometers). Rarely, the intrusive maybe mafic (diabase, gabbro, or syenite), especially at iron deposits.
2. Contact metamorphism (dehydration and decarbonation) of the country rocks occurs at 700-500° C, and results in a volume decrease. Crystallization of the intrusive proceeds to completion.
3. Early anhydrous zoned skarn formation occurs at 600-400° C, due either to the release of iron and silica-rich fluids from the magma, or to the arrival of fluids from a deeper source. In limestones, the dominant early skarn minerals are commonly garnet and/or clinopyroxene; in dolomite forsterite and/or phlogopite.
4. Metalliferous ore deposition commences at 500•300° C, as skarn formation continues. Scheelite and oxides generally appear to be earlier than associated sulfides. Ore: deposition is confined to earlier-formed skarn, some of which remains barren.
5. Late hydrothermal alteration occurs at 400-200° C or lower, with destruction of early anhydrous skarn minerals and continued ore deposition. Serpentine replaces forsterite, and calcite, magnetite, hematite, quartz, pyrite, ilvaite, chlorite, and other minerals replace garnet and clinopyroxene.

The geological structure of Elba with its variety of nappes and rocks of both oceanic and continental environment, is formed as a consequence of the Oligo-Miocene Apenninic collisional phase. After the collision, Elba was affected by polyphase extensional tectonics. The classic work of Trevisan (1950) divides the east-vergent nappe stack of Elba into 5 complexes.
Complexes I to III are composed of Late Paleozoic to Mesozoic rocks. They belong to the continental Tuscan Unit, which represents the western margin of the Adriatic microplate. The cover sequence of the basement includes middle to upper Triassic siliciclastic-terrestrial sediments, evaporites and shallow marine carbonates. These sediments pass into a Jurassic sequence, which was deposited on a subsiding passive continental margin. Metamorphism up to greenschist facies affected parts of the Tuscan units during Late Oligocene deformation. Complexes IV and V belong to the oceanic Ligurian Unit. Complex IV is made up of a Jurassic ophiolitic sequence and its sedimentary cover, whereas Complex V consists of rootless Cretaceous and Eocene flysch sediments. In the latest Miocene, during extension in the course of the opening of the Tyrrhenian Sea, two plutons intruded into the nappe stack (Serri et al.,1991).

Western Elba is dominated by the granodioritic Monte Capanne pluton, dated by the U/Pb method on zircons at 6.2 ± 0.2 Ma. In eastern Elba, a shallow quartzmonzonitic intrusion Porto Azzurro pluton, is dated by the K/Ar method at 5.9 ± 0.5 Ma. The Porto Azzurro pluton is slightly younger and as well as the Monte Capanne pluton emplaced in the upper crust and associated with top-to-the-east asymmetric extension.

Mappa geologica dell’Elba in cui vengono riportati i complessi intrusivi e i complessi tettonici, Modificata Da Rocchi et al. 2010.

The iron ore deposits, located in a N-S oriented belt along the east coast, are those of Ginevro, Sassi Neri, Capo Calamita, Terra Nera, Rio Marina and Rio Albano. They occur in different rock types and tectonic positions of the Tuscan Complexes.

Three major types of ore deposits in eastern Elba can be distinguished:

1) The magnetite-bearing Calamita-type deposits are located on the Calamita Peninsula. They are associated with ilvaite-ferrosalite-ferroactinolite-grossular-epidote-skarns. The lenticular ore bodies of over 100 m length and 60 m thickness close to the (Miocene) eastern Elba intrusive body belong to the tectonic complexes I and II (Ginevro, Sassi Neri and Capo Calamita).
2) The Ortano-type deposits are located in the central part of the eastern coast of Elba. They are represented by the pyrite-hematite-magnetite deposits of Rio Ortano and Terra Nera. A meter-sized skarn body is surrounded by unskarnified cataclastite of the Zuccale Detachment Fault in the Terra Nera deposit.
3) The Rio Marina-type includes the pyrite-hematite deposits of Rio Marina and Rio Albano. The lenticular ore bodies are hosted by Permo-Carboniferous rocks and rocks of the Verrucano Formation. These deposits are further differentiated into stratiform mineralizations in rocks of the Triassic terrestrial Verrucano Formation, hematite-pyrite masses in Carboniferous rocks and the Verrucano Formation, and in hematite veinlets related to late tectonic fractures. A sizeable skarn body is found one kilometer south of the Rio Marina deposit.

Sassi Neri Mine

The setting of the Miniera Sassi Neri, approx. 1.5 km north of the Ginevro deposit, is almost identical to that of the Ginevro deposit. Massive skarn mineralizations are surrounded by lowgrade metamorphic Calamita Schists. The skarn areas of Ginevro and Sassi Neri differ from all other Elbanean skarns. The amphibole (Fe-Pargasite) dominated skarns are characterized by veinlets (with bleached quartz-bearing rims and epidote minerals in the center), penetrating the surrounding Calamita Schists. Along fractures and other fluid migration paths the mafic components (mainly mica) of the Calamita Schists have been removed.
An aplitic dike, impregnated by iron ore and amphibole, is found in the western part of the Sassi Neri deposit. Like in Ginevro, relict pre-metasomatic structures or primary carbonates were not observed in the entire area. Massive magnetite is locally associated with pyrite, pyrrhotite and small crystals of epidote, adularia, sphene and quartz. Two generations of magnetite can be distinguished : Older euhedral, zoned crystals with minor partial resorption. Magnetite of the second generation is younger than the amphibole and forms xenomorphic, unzoned crystals. This magnetite II, encloses remnants of pyrrhotite and chalcopyrite. Pyrite is the youngest phase and of minor importance (in comparison with the northern deposits).

Sassi Neri Mine

Sassi Neri Mine. Granitic Dyke partially replaced by Pargasite skarn.

Pargasite Skarn from Sassi neri.

Bibliography

• L.D. Meinert; G.M.Dipple; S. Nicolescu: orld Skarn Deposits. Economic Geology 100th Anniversary Volume pp. 299–336
• Ines Dunkel: The Genesis of East Elba Iron Deposits and Their interrelation with messinian tectonics.

Photo

Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)
Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)
Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)
Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 2x (Field of view = 7mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)
Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)
Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 10x (Field of view = 2mm)
Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 10x (Field of view = 2mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)
Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 10x (Field of view = 2mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)
Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 10x (Field of view = 2mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 10x (Field of view = 2mm)
Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)
Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 2x (Field of view = 7mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 2x (Field of view = 7mm)
Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)
Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 2x (Field of view = 7mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 2x (Field of view = 7mm)	Fe-Pargasite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 2x (Field of view = 7mm)
Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)
Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 2x (Field of view = 7mm)	Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 2x (Field of view = 7mm)
Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 2x (Field of view = 7mm)	Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 2x (Field of view = 7mm)
Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 2x (Field of view = 7mm)	Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)
Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 2x (Field of view = 7mm)	Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). XPL image, 2x (Field of view = 7mm)
Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)	Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)	Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)
Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)	Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)	Fe-Pargasite and magnetite crystals in a Skarn from Sassi Neri mine, Elba (Italy). PPL image, 10x (Field of view = 2mm)