(public display, Geology Department, Wittenberg University, Springfield, Ohio, USA)
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"Glomeroporphyritic" is an odd term that refers to igneous rocks having a mix of large crystals (phenocrysts) and small crystals (groundmass). In glomeroporphyritic rocks, the phenocryst masses are bundled, intergrown crystals.
Lithology & geologic unit & age & locality: unrecorded/undisclosed
Tags: glomeroporphyritic igneous rock rocks
(public display, Geology Department, Wittenberg University, Springfield, Ohio, USA)
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"Glomeroporphyritic" is an odd term that refers to igneous rocks having a mix of large crystals (phenocrysts) and small crystals (groundmass). In glomeroporphyritic rocks, the phenocryst masses are bundled, intergrown crystals.
Lithology & geologic unit & age & locality: unrecorded/undisclosed
Tags: glomeroporphyritic igneous rock rocks
Coastal Oregon includes many outcrops of Tertiary-aged volcanic rocks. The sample seen here was eroded from the Yachats Basalt, a volcanic succession erupted from a Late Eocene-aged volcano. The sequence is mostly basalt lava flows, but includes some andesite and trachyandesite. Igneous dikes are also present - most are basalt, plus minor andesite and rhyodacite.
Basaltic flows in the Yachats Basalt are often porphyritic, with labradorite plagioclase feldspar phenocrysts. The glomeroporphyritic variety seen here has clusters of blade-shaped plagioclase phenocrysts.
Provenance: eroded from the Yachats Basalt, Upper Eocene, ~36-37 Ma
Locality: cobble on sandy-gravelly beach at Heceta Head, coastal Oregon, USA (vicinity of 44° 08' 02.18" North latitude, 124° 07' 24.58" West longitude)
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Some info. from:
Snavely & MacLeod (1974) - Yachats Basalt - an Upper Eocene differentiated volcanic sequence in the Oregon Coast Range. Journal of Research of the United States Geological Survey 2: 395-403.
Tags: glomeroporphyritic basalt Yachats Eocene Heceta Head Oregon volcanic volcanics lava
Coastal Oregon includes many outcrops of Tertiary-aged volcanic rocks. The sample seen here was eroded from the Yachats Basalt, a volcanic succession erupted from a Late Eocene-aged volcano. The sequence is mostly basalt lava flows, but includes some andesite and trachyandesite. Igneous dikes are also present - most are basalt, plus minor andesite and rhyodacite.
Basaltic flows in the Yachats Basalt are often porphyritic, with labradorite plagioclase feldspar phenocrysts. The glomeroporphyritic variety seen here has clusters of blade-shaped plagioclase phenocrysts.
Provenance: eroded from the Yachats Basalt, Upper Eocene, ~36-37 Ma
Locality: cobble on sandy-gravelly beach at Heceta Head, coastal Oregon, USA (vicinity of 44° 08' 02.18" North latitude, 124° 07' 24.58" West longitude)
----------------------------------------------
Some info. from:
Snavely & MacLeod (1974) - Yachats Basalt - an Upper Eocene differentiated volcanic sequence in the Oregon Coast Range. Journal of Research of the United States Geological Survey 2: 395-403.
Tags: glomeroporphyritic basalt Yachats Eocene Heceta Head Oregon volcanic volcanics lava
Coastal Oregon includes many outcrops of Tertiary-aged volcanic rocks. The sample seen here was eroded from the Yachats Basalt, a volcanic succession erupted from a Late Eocene-aged volcano. The sequence is mostly basalt lava flows, but includes some andesite and trachyandesite. Igneous dikes are also present - most are basalt, plus minor andesite and rhyodacite.
Basaltic flows in the Yachats Basalt are often porphyritic, with labradorite plagioclase feldspar phenocrysts. The glomeroporphyritic variety seen here has clusters of blade-shaped plagioclase phenocrysts.
Provenance: eroded from the Yachats Basalt, Upper Eocene, ~36-37 Ma
Locality: cobble on sandy-gravelly beach at Heceta Head, coastal Oregon, USA (vicinity of 44° 08' 02.18" North latitude, 124° 07' 24.58" West longitude)
----------------------------------------------
Some info. from:
Snavely & MacLeod (1974) - Yachats Basalt - an Upper Eocene differentiated volcanic sequence in the Oregon Coast Range. Journal of Research of the United States Geological Survey 2: 395-403.
Tags: glomeroporphyritic basalt Yachats Eocene Heceta Head Oregon volcanic volcanics lava