phenocryst

Vesicular andesite (Upper Pliocene, 1.9 Ma; Sierra Grande Shield Volcano, Raton-Clayton Volcanic Field, New Mexico, USA) 1
by James St. John

Anorthoclase crystals from kenyte lava (Late Pleistocene or Holocene; summit cone of Mt. Erebus Volcano, Ross Island, Antarctica) 1
by James St. John

Black porphyritic dacite (upper Holocene, 14 May 1915; Devastated Area, Lassen Volcano National Park, California, USA) 8
by James St. John

Vesicular porphyritic olivine basalt (31 January to 19 February 1960 Kapoho Eruption; town of Kapoho, Puna Rift Zone, Kilauea Volcano, easternmost Hawaii, USA)
by James St. John

Hot Creek (Long Valley Caldera, California, USA) 9
by James St. John

Hot springs & Hot Creek (Long Valley Caldera, California, USA) 18
by James St. John

Porphyritic dacite (Clear Creek, Shasta County, California, USA)
by James St. John

Wizard Island Cinder Cone (Holocene, ~7.2 ka; Crater Lake Caldera, Oregon, USA) 22
by James St. John

Wizard Island Cinder Cone (Holocene, ~7.2 ka; Crater Lake Caldera, Oregon, USA) 21
by James St. John

Vesicular porphyritic trachyte (Magadi Trachyte (Plateau Trachyte), Pleistocene, 700 ka to 1.4 Ma; northern end of Lake Magadi, Kenya Rift segment of the East African Rift Valley)
by James St. John

Wyomingite lamproite (Lower Pleistocene, 0.95 Ma; quarry on volcanic cone on Zirkel Mesa, Leucite Hills Volcanic Province, Wyoming, USA) 1
by James St. John

Sunstone (Tertiary; Spectrum Mine, Oregon, USA) 11
by James St. John

Dacite pumice (August 2006 eruption of Home Reef Volcano, Tofua Volcanic Arc, central Tonga Islands, sw Pacific Ocean; collected at beach in northern Fiji Islands) 2
by James St. John

Dacite pumice (August 2006 eruption of Home Reef Volcano, Tofua Volcanic Arc, central Tonga Islands, sw Pacific Ocean; collected at beach in northern Fiji Islands) 3
by James St. John

Natrocarbonatite (1963 pahoehoe lava flow, Old Doinyo Lengai Volcano, East African Rift Valley, northern Tanzania)
by James St. John

Porphyritic andesite (Sugarloaf Intrusion, Kate Peak Formation, Middle Miocene; Sugarloaf Hill, Six Mile Canyon, east of Virginia City, Nevada, USA)
by James St. John

Rhyolitic perlite (Yellowstone, Wyoming, USA)
by James St. John

Vesicular tholeiitic olivine basalt (Boring Volcanic Field, Upper Pliocene, probably ~3 Ma; Crown Point roadcut, Multnomah County, Oregon, USA) 2
by James St. John

Dacite pumice (August 2006 eruption of Home Reef Volcano, Tofua Volcanic Arc, central Tonga Islands, sw Pacific Ocean; collected at beach in northern Fiji Islands) 1
by James St. John

Hot Creek Rhyolite Flow (Pleistocene, 288 or 333 ka; Hot Creek Gorge, Long Valley Caldera, California, USA) 7
by James St. John

Porphyritic anorthoclase phonolite (Pleistocene; southern slopes of Mt. Kenya Volcano, south-central Kenya, East African Rift Valley)
by James St. John

Gray porphyritic dacite (Upper Pleistocene, 27 ka; Devastated Area, Lassen Volcano National Park, California, USA)
by James St. John

Alkaline picrite (Yuzhnoe Intrusion, Jurassic-Cretaceous boundary time, 145 Ma; Jetty Peninsula, western side of the Lambert Glacier, East Antarctica)
by James St. John

Minette (Upper Oligocene, 25 Ma; Narbona Pass Maar Volcano, summit of Chuska Mountains, Navajo Volcanic Field, New Mexico, USA) 2
by James St. John

Vesicular to pumiceous olivine orendite lamproite lava with xenoliths (Lower Pleistocene, 1.30 to 1.37 Ma; Black Rock, eastern Leucite Hills Volcanic Province, northeast of the town of Superior, southwestern Wyoming, USA)
by James St. John

Hot Creek Rhyolite Flow (Pleistocene, 288 or 333 ka; Hot Creek Gorge, Long Valley Caldera, California, USA) 42
by James St. John

Porphyritic leucite lava (possibly phonolite) (Rome, Italy) 2
by James St. John

Crater Lake Caldera & Mount Scott Volcano (Oregon, USA) 2
by James St. John

Aphyric & partially devitrified rhyolitic obsidian (Roaring Mountain Member, Plateau Rhyolite, Upper Pleistocene, ~59 ka; Obsidian Cliff, Yellowstone, Wyoming, USA) 1
by James St. John

Kimberlite (Gates-Adah Kimberlite Dike, Early Jurassic; Fayette County, Pennsylvania, USA) 2
by James St. John

Pumiceous orendite lamproite lava with xenolith (Lower Pleistocene, 1.30 to 1.37 Ma; Black Rock, eastern Leucite Hills Volcanic Province, northeast of the town of Superior, southwestern Wyoming, USA)
by James St. John

Crater Lake Caldera & Mount Scott Volcano (Oregon, USA) 1
by James St. John

Porphyritic basalt (5.3 cm across)
by James St. John

Wizard Island Cinder Cone (Holocene, ~7.2 ka; Crater Lake Caldera, Oregon, USA) 36
by James St. John

Wizard Island Cinder Cone (Holocene, ~7.2 ka; Crater Lake Caldera, Oregon, USA) 11
by James St. John

Ugandite (Indaiá II Intrusion, Alto Paranaíba Igneous Province, Late Cretaceous, 80-90 Ma; near Rio Perdizos, Minas Gerais State, Brazil)
by James St. John

Minette (Upper Oligocene, 25 Ma; Narbona Pass Maar Volcano, summit of Chuska Mountains, Navajo Volcanic Field, New Mexico, USA) 1
by James St. John

"Imperial Porphyry" - porphyritic metadacite to porphyritic meta-andesite (Dokhan Volcanics, Neoproterozoic, ~593-602 Ma; Mons Porphyrites, Red Sea Mountains, Egypt) 2
by James St. John

Kenyte (porphyritic anorthoclase phonolite) (Pleistocene; southern slopes of Mt. Kenya Volcano, south-central Kenya, East African Rift Valley)
by James St. John

Vesicular olivine orendite lamproite lava (Lower Pleistocene, 1.30 to 1.37 Ma; Black Rock, eastern Leucite Hills Volcanic Province, northeast of the town of Superior, southwestern Wyoming, USA) 2
by James St. John

Rhyolite (Palisade Rhyolite, North Shore Volcanic Group, Mesoproterozoic, 1096-1097 Ma; Rt. 1 roadcut just north of Ilgen City, Minnesota, USA) 2
by James St. John

Wyomingite (Lower Pleistocene, 0.95 Ma; quarry on volcanic cone on Zirkel Mesa, Leucite Hills Volcanic Province, Wyoming, USA) 3
by James St. John

Andesite (1997 lava from Soufriere Hills Volcano, Montserrat, Lesser Antilles Volcanic Arc, eastern Caribbean Sea) 3
by James St. John

Porphyritic rhyolite (Pleistocene; Yellowstone, Wyoming, USA)
by James St. John

Wizard Island Cinder Cone (Holocene, ~7.2 ka; Crater Lake Caldera, Oregon, USA) 14
by James St. John

Nara Brown Granite (charnockite/farsundite/quartz mangerite) (Riviere-a-Pierre Plutonic Suite, Mesoproterozoic, ~1.1 Ga; north of Riviere-a-Pierre, Quebec, Canada)
by James St. John

Wizard Island Cinder Cone (Holocene, ~7.2 ka; Crater Lake Caldera, Oregon, USA) 10
by James St. John

Black Rock (Lower Pleistocene olivine orendite lamproite volcanic center in the Leucite Hills, Wyoming, USA) 2
by James St. John

Rhyolitic vitrophyre (Banco Bonito Obsidian, Upper Pleistocene, 50-55 ka; Three Rhyolites Roadcut, Rt. 4, southern margin of Valles Caldera, northern New Mexico, USA)
by James St. John

Trachyte obsidian (Quaternary; Ol Doinyo Nyukie Volcano, Kenya) 1
by James St. John

Llanite (porphyritic melarhyolite) (Mesoproterozoic, 1.106 Ga; roadcut ~9 miles north of Llano, Texas, USA) 2
by James St. John

Kimberlite-wall rock sample (Gates-Adah Kimberlite Dike, Early Jurassic; Fayette County, Pennsylvania, USA)
by James St. John

Porphyritic nepheline syenite (float boulder from summit spires of Mt. Kenya Volcano, south-central Kenya, East African Rift Valley)
by James St. John

Hyalite opal on vesicular porphyritic leucite tephrite (Doupov Volcanic Complex, Oligocene to Lower Miocene; hills of the Doupov Mountains, north or west of Valec (Waltsch), northwestern Bohemia) 1
by James St. John

Porphyritic leucite lava (Caprarola, Vico Lake, Viterbo, Italy) 5
by James St. John

Blairmorite (porphyritic analcime phonolite) (Crowsnest Volcanics, mid-Cretaceous, 100 Ma; near Blairmore, Alberta, Canada) 2
by James St. John

Andesite
by James St. John

Rhyolitic volcanic tuff (Grassy Mountain Ignimbrite, Mesoproterozoic; near Rosselle, Missouri, USA)
by James St. John

Wizard Island Cinder Cone (Holocene, ~7.2 ka; Crater Lake Caldera, Oregon, USA) 18
by James St. John

Porphyritic diabase (Cape Ann, Massachusetts, USA) 2
by James St. John