The word "thomselonite" is a mineral name, and its spelling is determined by the International Mineralogical Association. Phonetically, it is spelled /θɒmˈsɛlənaɪt/. This word contains the phonetic symbols "θ" which represents the "th" sound, "ɒ" which represents the "o" sound, and "ə" which represents the "uh" sound. The "na" in "thomselonite" is pronounced as "nuh" and is represented by the symbol "nə". Overall, the spelling of "thomselonite" accurately reflects its pronunciation and helps to ensure clear communication.
I apologize, but I couldn't find a dictionary definition for the term "thomselonite." It's possible that it may be a relatively unknown or specialized term that has not yet been included in mainstream dictionaries.