Optical Mineralogy (Open Textbook)
by Dexter Perkins, Matt Kohn, John Brady · OpenGeology / NSF-supported
Fifteen-chapter open reference for identifying minerals in thin section under a petrographic microscope, organised by mineral group, with extensive photographs, rotation videos showing optical variability, and a procedure for working through unknown grains. Laboratory identification is a distinct hands-on skill from field identification, and this is the free resource that teaches it with real photographs and rotation video rather than idealised diagrams.
More resources on Mineralogy
Rocks & Minerals (Smithsonian Handbook)
Pocket field guide to more than 500 rocks and minerals, organised by chemical class, with 600 photographs of cut specimens against a plain ground and side-by-side notes on hardness, cleavage, lustre, streak and distinguishing features. Hands-on identification is a real skill in this topic and this is the guide rockhound and geology communities converge on: organised by mineral chemistry rather than by colour, so it teaches classification while being used, and photographed consistently enough to actually match specimens.
Introduction to Mineralogy (3rd Edition)
University textbook merging traditional and optical mineralogy, treating crystallography, chemical bonding, controls on mineral structure, mineral stability and crystal growth, then describing the rock-forming mineral groups within their geologic and petrologic context.
Mineralogy (Open Textbook)
Free college-level textbook in fourteen chapters covering mineral chemistry and properties, crystallography and symmetry, X-ray diffraction, and the igneous, sedimentary, metamorphic and ore mineral groups, with over 1,200 figures and a mineral encyclopedia. This is the spine a self-learner reads front to back.
Handbook of Mineralogy
Five-volume reference from the Mineralogical Society of America giving one-page data sheets for roughly 1,000 mineral species: crystal data, physical and optical properties, X-ray powder patterns, chemistry, occurrence, and literature citations. Free searchable PDFs.
Mindat.org — The Mineral Database
Community-curated database of every IMA-approved mineral species, with crystallographic data, physical properties, photographs, and over 300,000 documented occurrences across roughly 68,000 localities worldwide. The single highest-leverage free reference in mineralogy — species data, chemistry, crystal systems, photographs, and locality records in one place. Run by the non-profit Hudson Institute of Mineralogy since 2000.