Earth Science WWW Resources
I started maintaining lists of Earth Science resources in about 1996, when the Web was fairly young. It's so much easier today to find resources, and a lot harder for a compiler to keep track of them, so I've given up any attempt to provide this kind of coverage. Nevertheless, here are a few things you might not find right away with a search engine.
Petrological blogs
Metageologist
http://all-geo.org/metageologist/
Alias Simon Wellings, alumnus of what has become the Oxford Hard Rock Group
Life in Plane Light: The microscope is my friend
http://lifeinplanelight.wordpress.com/
Mountain Beltway - metamorphism category
http://blogs.agu.org/mountainbeltway/category/metamorphism/
Between a Rock and a Hard Place - Bristol University PhD students
http://betweenarock.co.uk/, or
http://blogs.egu.eu/bar/
VOLCANICDEGASSING - mainly about volcanoes
http://volcanicdegassing.wordpress.com/
There are several volcanology blogs out there but this is an ad for
an Oxford colleague and research group
All-geo: The best of Geology and Earth Science on the web
http://all-geo.org/
Keep up to date; maybe there's some hard-rock petrology out there
Petrographic images
Kurt Hollocher's Metamorphic Minerals Image Gallery
http://minerva.union.edu/hollochk/c_petrology/met_minerals.htm
A nice selection of high-quality photomicrographs
See his Igneous and Metamorphic Petrology index page
http://minerva.union.edu/hollochk/c_petrology/index.htm
for more photo galleries
The Virtual Microscope (developed by the Open University)
http://www.virtualmicroscope.org/
http://www.virtualmicroscope.org/content/uk-virtual-microscope
Thin section and hand specimen images, excellent
GigaPan - Geological thin sections gallery
http://gigapan.com/galleries/7729
Big images, but of variable quality
PetrographypediA
http://www.petrographypedia.com/pedia/Main_Page
Atlas de Mineralogía Óptica (in Spanish)
http://www.ehu.es/mineralogiaoptica/Atlas_de_Mineralogia_Optica/Atlas_de_Mineralogia_Optica.html
Nice! Be patient while the images load.
Atlas of Igneous and Metamorphic Rocks, Minerals and Textures
http://leggeo.unc.edu/Petunia/IgMetAtlas/mainmenu.html
1990s site, still there!
Microckscopica - Bernardo Cesare's Rock Art project
http://microckscopica.altervista.org/en/
Psychedelia made from metamorphic and igneous rock thin sections
Other metamorphic rock images
GigaPan - from the Geology category
http://gigapan.com/gigapans?tags=metamorphic
For giant images of metamorphic rocks in the field or in hand specimen