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Diabase Sills, Mojave Desert, California
The green-colored rock in this photo is a 1 billion year old intrusion called diabase (chemically similar to basalt). Because it intrudes parallel to the layering in the country rock, it is called a sill. The country rock is the Proterozoic Crystal Spring Formation. Throughout the Death Valley region, talc deposits formed at the contact of the diabase sills and dolomite of the Crystal Spring Formation. Death Valley National Park. (Ig-21)
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Diorite sill (Purcell sill), Montana
Diorite sill (Purcell sill) intruding Precambrian Belt Supergroup. Note bleached zone on either side of sill that formed by contact metamorphism. Glacier National Park, Montana. (Ig-24)
Download ImageDiabase sill in marble, California
Diabase sill in marble, southern Death Valley National Park, California. Note the talc on the left side of the image. Ig-20.
Download ImagePegmatite dike in granitic rock.
Note chilled margin, defined by the finer grained quartz and K-feldspar crystals along the margin of the dike. (Ig-18)
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Phreatic explosion craters, Death Valley, CA.
Aerial view of phreatic explosion craters. Little Hebe Craters, Death Valley National Park, California. (Ig-106)
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Composite dike
Dioritic inclusions in granitic dike intruding slate, southern British Columbia, Canada. (Ig-16)
Download ImageMafic dike and sill intruding marble.
Diabase dike and sill intruding marble, Death Valley, California.
Download ImageGranitic apophyses intruding gneiss, NV.
Apophyses of granitic rock intruding gneiss, Nevada.
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Phreatic explosion crater. Death Valley, CA.
Phreatic explosion crater. Ubehebe Crater, Death Valley National Park, California. (Ig-107).
Download ImageMetamorphosed pillow basalt (vertical)
Metamorphosed pillow basalt (Purcell Lavas–greenstone), Glacier National Park, Montana. (Ig-105)
Download ImageMafic dike cutting sedimentary rock.
Mafic dike intruding sedimentary rock, SE California. (Ig-12)
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Phreatic explosion craters. Death Valley, CA
Aerial view of Ubehebe Craters, a small field of some 13 phreatic explosion craters, the largest of which is Ubehebe Crater itself. These craters formed when rising basaltic magma encountered groundwater and flashed to steam. (Ig-108).
Download ImageVolcanic rock thin section
Photomicrograph of basalt showing plagioclase phenocrysts. (Ig-101)
Download ImagePahoehoe lava, Hawaii. (vertical)
Active basaltic lava flow on Kilauea volcano, Hawaii. (Ig-103)
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