The term "gemmology" with a double "m" is the original spelling and has been in use since the mid-19th century. The word is derived from the Latin word "gemma," which means "precious stone" or "jewel," and the Greek word "logos," which means "word" or "study."
The founder of the GIA, Robert M. Shipley, is often credited with changing the spelling of "gemmology" to "gemology" in the United States.
Shipley believed that the double "m" in "gemmology" was a holdover from British English and that the single "m" spelling would be more appropriate for American English.
However, it's worth noting that the spelling of "gemology" with one "m" was already in use in some American publications prior to Shipley's involvement with the field.
Shipley himself acknowledged this in his book "Gemology," in which he wrote,
"The term 'gemology' with one 'm' has been used occasionally in this country since about 1910, but it was not until 1930 that the term was brought to the attention of the trade in a more forceful manner."
So while Shipley may have popularised the spelling of "gemology" with one "m" in the United States, he did not necessarily invent or originate the spelling.
FUN FACT
The term "gemmology" was first used in the book "The Natural History of Precious Stones and Precious Metals" by the British mineralogist and author Edward William Cooke.
The book was published in London in 1880.
Summary
While both spellings are now accepted and widely used, "gemmology" with a double "m" remains the more common spelling outside of the United States, particularly in British English and other varieties of English influenced by British usage.