Webmineral.com
Unknown
A long-running mineral reference database listing several thousand species with chemical formulas, crystallographic data, X-ray diffraction patterns and optical constants. Useful for identifying an unknown sample or checking physical property values while working through a mineralogy course.
More resources on Mineralogy & Petrology
mindat.org
Mindat.org is a comprehensive, community-curated mineral database offering detailed mineral data sheets, locality information with maps, and extensive photos and educational resources for learning mineralogy and petrology.
Mineralogy Database
The Mineralogical Society of America's Handbook of Mineralogy, free as searchable PDFs. Each entry gives crystal system, optical and physical properties, occurrence and type localities, so students can look up authoritative reference data for individual mineral species.
Earth Materials
Cambridge University Press textbook covering mineralogy and petrology together in one illustrated volume. Working through it, students learn to identify common rock-forming minerals, read phase diagrams, and explain how igneous, sedimentary and metamorphic rocks record the processes that formed them.
Minerals
A concise optical mineralogy reference covering how 58 common minerals appear under a petrographic microscope, with color plates of each. After working through it you can identify rock-forming minerals in thin section by their optical properties.
rruff.info
RRUFF is an open-access mineralogy and petrology database. It provides Raman and infrared spectra, X-ray diffraction patterns, crystal structures, chemical analyses, and curated references for mineral identification and research.