Emery from the Tertiary of Naxos Island, Greece. (~4.4 centimeters across along the base)
Emery is a rare metamorphic rock. Also known as corundite, the rock is dominated by the mineral corundum, a very hard aluminum oxide, Al2O3. Corundum is the definition of hardness 9 on the Mohs Hardness Scale.
This material comes from the Naxos Emery Deposits on the island of Naxos in the Aegean Sea. Naxos is dominated by metamorphic rocks and some igneous rocks. Much of the island consists of marbles (originally limestones). Some of the original limestones had lenses of bauxite, a rock having aluminum hydroxy-oxide minerals. Upon metamorphism, the limestones were converted to marbles and the bauxites were converted to diasporites (= diaspore (AlO·OH)-dominated rocks).
With further metamorphism, the diasporites were converted to corundites plus water. High fluid pressures fractured the rocks, and the fractures got filled up with corundite.
Metamorphism on Naxos occurred during the Cenozoic in two main phases. A high-grade metamorphic event occurred during the Eocene, at about 40-50 million years ago. A second, intermediate-grade metamorphic event occurred during the Early Miocene, at 16-20 million years ago.
The "quality" of emery in the Naxos Emery Deposits varies from relatively pure corundite, which can be blue (= sapphire rock) to corundite significantly mixed with other minerals. This emery specimen is magnetitic corundite - a magnet sticks to it.
The brownish coloration facing the viewer is iron oxide staining along a fracture surface.
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Info. synthesized from:
Urai & Feenstra (2001) - Weakening associated with the diaspore-corundum dehydration reaction in metabauxites: an example from Naxos (Greece). Journal of Structural Geology 23: 941-950.
Feenstra & Wunder (2002) - Dehydration of diasporite to corundite in nature and experiment. Geology 30(2): 119-122.
Tags: corundite emery magnetite magnetic Naxos Aegean Sea Tertiary Eocene Mioene Greece
Emery from the Tertiary of Naxos Island, Greece. (~5.6 centimeters across along the base)
Emery is a rare metamorphic rock. Also known as corundite, the rock is dominated by the mineral corundum, a very hard aluminum oxide, Al2O3. Corundum is the definition of hardness 9 on the Mohs Hardness Scale.
This material comes from the Naxos Emery Deposits on the island of Naxos in the Aegean Sea. Naxos is dominated by metamorphic rocks and some igneous rocks. Much of the island consists of marbles (originally limestones). Some of the original limestones had lenses of bauxite, a rock having aluminum hydroxy-oxide minerals. Upon metamorphism, the limestones were converted to marbles and the bauxites were converted to diasporites (= diaspore (AlO·OH)-dominated rocks).
With further metamorphism, the diasporites were converted to corundites plus water. High fluid pressures fractured the rocks, and the fractures got filled up with corundite.
Metamorphism on Naxos occurred during the Cenozoic in two main phases. A high-grade metamorphic event occurred during the Eocene, at about 40-50 million years ago. A second, intermediate-grade metamorphic event occurred during the Early Miocene, at 16-20 million years ago.
The "quality" of emery in the Naxos Emery Deposits varies from relatively pure corundite, which can be blue (= sapphire rock) to corundite significantly mixed with other minerals. This emery specimen is magnetitic corundite - a magnet sticks to it.
-------------
Info. synthesized from:
Urai & Feenstra (2001) - Weakening associated with the diaspore-corundum dehydration reaction in metabauxites: an example from Naxos (Greece). Journal of Structural Geology 23: 941-950.
Feenstra & Wunder (2002) - Dehydration of diasporite to corundite in nature and experiment. Geology 30(2): 119-122.
Tags: corundite emery magnetite magnetic Naxos Aegean Sea Tertiary Eocene Mioene Greece
(wet, cut surface)
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"Greek Green Porphyry" is a famous, classic decorative stone that rivals "Imperial Porphyry" in importance. The rock itself is a Triassic, subvolcanic, glomeroporphyritic metabasalt with light-colored, saussuritized (altered) plagioclase feldspar phenocrysts, blackish pyroxene phenocrysts, and a dark greenish, finely-crystalline groundmass. Minerals identified in the groundmass include albite feldspar, augite pyroxene, epidote, magnetite, quartz, titanite / sphene, and chlorite.
Published geochemistry details show that this material is porphyritic basalt, later subjected to low-grade metamorphism. Silica percentages are ~53-54%, numbers that prompted some to categorize "Green Green Porphyry" as porphyritic andesite. The relatively high silica numbers resulted from partial silicification. This rock is actually transitional between tholeiitic basalt and calc-alkaline volcanics.
"Greek Green Porphyry" is known by many names, including:
Lapis Taygetas
Marmo Taigeto
Lapis Croceus
Krokeatis Lithos
Krokeian Stone
Marmo Tenario
Lapis Spartanus
Marmo Spartano
Lapis Lacedaemonius
Marmor Lacedaemon
Marmo Lacedemonio
Marmo Verde Lacedomonio
Marmo Laconio
Porfido Verde Antico [despite it not being serpentinite]
Porfido Serpentino Verde [despite it not being serpentinite]
Laconian emerald
Stratigraphy: Tyros Beds, Phyllite-Quartzite Series, Triassic
Locality: near Levetsova / Krokees, Laconia, southern Peloponnese Peninsula, southern Greece
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Mostly synthesized from:
Koutsovitis et al. (2016) - Mineralogical, petrological and geochemical features of the unique Lapis Lacedaemonius (Krokeatis Lithos) from Laconia, Greece: approach on petrogenetic processes within the Triassic volcanic context. Bulletin of the Geological Society of Greece 50: 1903-1912.
Price (2007) - The Sourcebook of Decorative Stone, an Illustrated Identification Guide. Buffalo, New York. Firefly Books. 288 pp.
Tags: Greek Green Porphyry Triassic Tyros Beds Phyllite Quartzite Series Levetsova Krokees Laconia Peloponnese Peninsula Greece decorative stone stones Porfido Verde Antico Serpentino Lapis Lacedaemonius Croceus Spartanus Taygetas glomeroporphyritic porphyritic basalt metabasalt plagioclase phenocryst phenocrysts
Emery from the Tertiary of Naxos Island, Greece. (~5.6 centimeters across along the base)
Emery is a rare metamorphic rock. Also known as corundite, the rock is dominated by the mineral corundum, a very hard aluminum oxide, Al2O3. Corundum is the definition of hardness 9 on the Mohs Hardness Scale.
This material comes from the Naxos Emery Deposits on the island of Naxos in the Aegean Sea. Naxos is dominated by metamorphic rocks and some igneous rocks. Much of the island consists of marbles (originally limestones). Some of the original limestones had lenses of bauxite, a rock having aluminum hydroxy-oxide minerals. Upon metamorphism, the limestones were converted to marbles and the bauxites were converted to diasporites (= diaspore (AlO·OH)-dominated rocks).
With further metamorphism, the diasporites were converted to corundites plus water. High fluid pressures fractured the rocks, and the fractures got filled up with corundite.
Metamorphism on Naxos occurred during the Cenozoic in two main phases. A high-grade metamorphic event occurred during the Eocene, at about 40-50 million years ago. A second, intermediate-grade metamorphic event occurred during the Early Miocene, at 16-20 million years ago.
The "quality" of emery in the Naxos Emery Deposits varies from relatively pure corundite, which can be blue (= sapphire rock) to corundite significantly mixed with other minerals. This emery specimen is magnetitic corundite - a magnet sticks to it.
-------------
Info. synthesized from:
Urai & Feenstra (2001) - Weakening associated with the diaspore-corundum dehydration reaction in metabauxites: an example from Naxos (Greece). Journal of Structural Geology 23: 941-950.
Feenstra & Wunder (2002) - Dehydration of diasporite to corundite in nature and experiment. Geology 30(2): 119-122.
Tags: corundite emery magnetite magnetic Naxos Aegean Sea Tertiary Eocene Mioene Greece
Emery from the Tertiary of Naxos Island, Greece. (~5.9 centimeters across along the base)
Emery is a rare metamorphic rock. Also known as corundite, the rock is dominated by the mineral corundum, a very hard aluminum oxide, Al2O3. Corundum is the definition of hardness 9 on the Mohs Hardness Scale.
This material comes from the Naxos Emery Deposits on the island of Naxos in the Aegean Sea. Naxos is dominated by metamorphic rocks and some igneous rocks. Much of the island consists of marbles (originally limestones). Some of the original limestones had lenses of bauxite, a rock having aluminum hydroxy-oxide minerals. Upon metamorphism, the limestones were converted to marbles and the bauxites were converted to diasporites (= diaspore (AlO·OH)-dominated rocks).
With further metamorphism, the diasporites were converted to corundites plus water. High fluid pressures fractured the rocks, and the fractures got filled up with corundite.
Metamorphism on Naxos occurred during the Cenozoic in two main phases. A high-grade metamorphic event occurred during the Eocene, at about 40-50 million years ago. A second, intermediate-grade metamorphic event occurred during the Early Miocene, at 16-20 million years ago.
The "quality" of emery in the Naxos Emery Deposits varies from relatively pure corundite, which can be blue (= sapphire rock) to corundite significantly mixed with other minerals. This emery specimen is magnetitic corundite - a magnet sticks to it.
The dull brownish coloration facing the viewer is iron oxide staining along a fracture surface.
-------------
Info. synthesized from:
Urai & Feenstra (2001) - Weakening associated with the diaspore-corundum dehydration reaction in metabauxites: an example from Naxos (Greece). Journal of Structural Geology 23: 941-950.
Feenstra & Wunder (2002) - Dehydration of diasporite to corundite in nature and experiment. Geology 30(2): 119-122.
Tags: corundite emery magnetite magnetic Naxos Aegean Sea Tertiary Eocene Mioene Greece