Porphyritic metadacite to porphyritic meta-andesite from the Precambrian of Egypt. (photo provided by Karen van Opstal) “Imperial Porphyry” is a beautiful, important, historically-valuable decorative stone. It was initially quarried during the Egyptian Ptolemaic Dynasty and was also used in the Roman Empire. In later centuries, it was reused in southern and southeastern Europe. This rock type comes from quarries at Mons Porphyrites in eastern Egypt. The locality name is the basis for the petrologic term “porphyritic”, which refers to a mix of large and small crystals in an igneous rock. Imperial Porphyry rocks are dark reddish or dark purplish with light-colored feldspar phenocrysts. The red and purple colors are the result of alteration of the original rock, which is dark gray-colored. These rocks are part of the Dokhan Volcanics, a greater-than-1 kilometer thick succession of late Precambrian-aged, terrestrial, intermediate to felsic volcanic rocks (= lava flows, volcanic tuffs, and volcanic agglomerates). The nature, age, mineralogy, geochemistry, and paleotectonic setting of the Dokhan Volcanics indicate that Imperial Porphyry rocks are lava flows that accompanied subduction zone volcanism during the Pan-African Orogeny. Subduction was followed by a collision event along the Mozambique Belt in the late Precambrian, during which the ancient small supercontinent Gondwana formed (www.researchgate.net/figure/Map-of-the-Gondwana-supercont...). Gondwana was part of a larger supercontinent called Pannotia, which rifted apart in the latest Precambrian (upload.wikimedia.org/wikipedia/commons/d/d7/Pannotia.svg). Geochemical analysis of Imperial Porphyry rocks has shown that they are 62.2 to 64.4% silica, which makes them porphyritic quartz andesites and porphyritic dacites. A detailed mineral analysis of Imperial Porphyry is given in Makovicky et al. (2016). The mineralogy shows that the rocks have been subjected to fluid alteration and greenschist-facies metamorphism, possibly related to the Pan-African Orogeny and/or burial metamorphism and/or Red Sea rifting orogenesis. The reddish to purplish coloration is from partial hematitization of mafic minerals. Because the rocks are slightly metamorphosed, they are better referred to as "meta-andesite" and "metadacite". Stratigraphy: upper Dokhan Volcanics, Ediacaran, upper Neoproterozoic, ~593-602 Ma Locality: old Roman quarry at Mons Porphyrites, above Wadi Abu Maamel, Red Sea Mountains, Eastern Desert, eastern Egypt --------------------- Geologic info. mostly synthesized from: Makovicky et al. (2016) - Imperial Porphyry from Gebel Abu Dokhan, the Red Sea Mountains, Egypt, part I. mineralogy, petrology and occurrence. Neues Jahrbuch für Mineralogie Abhandlungen [Journal of Mineralogy and Geochemistry] 193: 1-27.
Laker
Pictures and descriptions on how to tell the difference between true agates and beach rocks that look like agates found along Lake Superior's beaches in Minnesota, Ontario, Michigan Upper Peninsula, and Wisconsin.
sorting a kingly number of pens, stripeys forever, shells cupping tiny pretties, and rusting big canvas too, thinking about journal covers and other possibilities... xox - eb.
#gelpress #gelplate #gelprinting #monoprint
Shop hippiegypsy3's closet or find the perfect look from millions of stylists. Fast shipping and buyer protection. This a clear glass globe that screws into a plastic stand which I have filled with beautiful agates and other rocks and stones from several different states here in the US. Great gift for the rock and gem collector - I think we all know one of those! or a center piece for your meditation table or alter.
Welcome! These are all agates that I own. Most I purchased at various rock shows or auctions. The eye agate I found myself (see #28). Most are Lake Superior agates (Lakers), but there are also Luguna, Dryhead, Fairburn, Botswana, and Brazil agates here. Don't miss the original sizes that are available for many of these images. Change to the Critique Style, and then under Other sizes click on the capital O. Enjoy! NOTE: For purposes of online presentation colors of agate specimens may be a bit more saturated than in reality. Did you know that God likes agates too? Besides the obvious (one who makes something so beautiful must of himself also enjoy it) we find in the Bible that God says part of the foundation of the walls of his heavenly city will be of agate (see Revelation 21:19). Don't just glory in the rock, glory in the one who made it - Becoming a Christian - A Quest for Joy.
MICHIGAN is rich in rocks, minerals and gemstones. It's what makes it a rock collectors ideal destination! Here's a list of minerals and gemstones found in Michigan.
One of two faces of a delicate, classic , Lake Superior, red and white, candy striped agate.
Geocaching is a treasure hunting game where you use a GPS to hide and seek containers with other participants in the activity. Geocaching.com is the listing service for geocaches around the world.
A Lake Superior agate ground into a sphere. Photo by Fluorite Of all the gems in the world agates are one of the most complicated e...
Thompsonite is the name of a series of tecto-silicate minerals of the zeolite group
Lake Superior Agates are found on the shores of Lake Superior. This agate is known for its numerous red bands which are iron stains. These iron rich minerals reflect the gemstone’s geologic history in Minnesota, Wisconsin and Michigan. In 1969. the Minnesota legislature designated the Lake Superior Agate as the official state gemstone. It was
Minnesota Mineral Club to Host 'Celebration of Agates' - Hopkins, MN - The event takes place July 26 to 29 at Hopkins High School.
Ricardo and Claudia, thanks for all your beautiful agates!!! 10,3 x 7 cm (13176)
You tell me. (Update 4-11-2011) This is a Lake Superior Thunderegg.
Sagenite and diamonds. Can it get any better?
