Andesite
Videos
Andesite is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained to porphyritic in textu
A sample of andesite (dark groundmass) with amygdaloidal vesicles filled with zeolite. Diameter of view is 8 cm.
QAPF diagram with basalt/andesite field highlighted in yellow. Andesite is distinguished from basalt by SiO2 > 52%.
Block lava at Fantastic Lava Beds near Cinder Cone in Lassen Volcanic National Park
Photomicrograph of andesite in thin section (between crossed polarizers)
Amphibole
Videos
Amphibole is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain SiO4 tetrahedra, linked at the vertices and generally containing ions of iron and/or magnes
Amphibole (tremolite)
Photomicrographs of a thin section containing an amphibole crystal; under cross-polarized light on the left, and plane-polarized light on the right.
![Double-chain inosilicate structure looking up the [100] axis. Silicon ions are hidden by apical oxygen ions.](https://upload.wikimedia.org/wikipedia/commons/thumb/d/d5/Amphibole_100.jpg/500px-Amphibole_100.jpg)
Double-chain inosilicate structure looking up the [100] axis. Silicon ions are hidden by apical oxygen ions.
![Side view (along [010]) of double chain inosilicate backbone. Apical oxygens are at the bottom.](https://upload.wikimedia.org/wikipedia/commons/thumb/b/b7/Amphibole_010.jpg/500px-Amphibole_010.jpg)
Side view (along [010]) of double chain inosilicate backbone. Apical oxygens are at the bottom.