heptaphyllite

noun

hep·​ta·​phyllite

¦heptə+

: any of a group of micas (as muscovite and other light-colored micas) with seven metallic ions per ten oxygen and two hydroxyl ions compare octaphyllite

Word History

Etymology

hepta- + phyllite

Love words?

You must — there are over 200,000 words in our free online dictionary, but you are looking for one that’s only in the Merriam-Webster Unabridged Dictionary.

Start your free trial today and get unlimited access to America's largest dictionary, with:

• More than 250,000 words that aren't in our free dictionary
• Expanded definitions, etymologies, and usage notes
• Advanced search features
• Ad free!