Just because the Merriam-Webster online dictionary does not recognize the word "sparkliest," doesn't mean it isn't a word.
Trenton Jewelers owner and jewelery designer Wayne McDermitt said he uses "sparkliest" to describe diamonds all the time.
For example, McDermitt considers one of his most expensive pieces of jewelery to be one of the "sparkliest" in the store.
McDermitt designed and made a three carat diamond ring with over one carat of diamonds in the setting--priced at $44,500.
McDermitt's said his three carat wonder is a hearts and arrows cut diamond of the finest quality with SI2 clarity and D color--which is another way of saying the diamond is visually flawless and has the highest degree of whiteness on the diamond grading scale. Which is good.
For more information on diamonds large and small contact Trenton Jewelers 734-676-0188.