A basalt is a fine-grained basic igneous rock containing essential calcic plagioclase feldspar and pyroxene (usually Augite), with or without olivine. Basalts can also contain quartz, hornblende, biotite, hypersthene (an orthopyroxene) and feldspathoids.

The Lunar and Planetary Institute hosts dozens of documentation photos of 12002 here and 12005 here, including photos of the hand samples from which they were cut.

This collection consists of the rocks and thin sections used in the Open University modules. The first set of samples are from the level 3 module Understanding the Continents. The theme of the module is crustal evolution in contrasting environments.

Click the microscope button to view a thin section for this sample. Click the object button to view an object rotation for this sample. This fine-grained basalt comes from the Isle of Staffa, which lies east of the Isle of Mull in the Inner Hebrides of Scotland.

Basalt constitutes the Earth's most abundant igneous rock type, estimated to comprise approximately 70% of the planet's crust. Basalt is defined as a fine-grained, dark-colored igneous rock composed mainly of plagioclase and pyroxene minerals, with or without olivine.

PPL thin section of a basalt consisting of randomly oriented crystals of colorless plagioclase, pale green augite, and opaque oxides from a dike neat Kintallen, Isle of Mull, Scotland. Zoom in and out with the scroll button or mouse pad, then pan with your mouse. Click on the "xpl" button to see a version of this image in cross polarized light.

micROCKscopic.ro makes Optical Mineralogy and Petrology be easier to examine a thin section and to understand the characteristic properties of each mineral/rock without a petrographic microscope, which is known to be very expensive.

The sample is a medium-grained basalt in thin section, consisting of a framework of plagioclase with pyroxene forming a poikilitic texture. There are patches of alteration that may once have been olivine or glass but are now entirely transformed to clay minerals and chlorite.

Information about and links to thin section phase maps of basalt volcanic igneous rocks

Basalt thin section in plane polarized light (PPL). Notice that it consists of several minerals: plagioclase laths (clear), clinopyroxene (beige), olivine (clear but equant), opaque minerals (magnetite and ilmenite), and "mesostasis" (partially devitrified glass).