Gravwacke or Grauwacke: How To spell?

The word Gravwacke is misspelled against Grauwacke, a noun meaning "Graywacke."

Word contains consecutive vowels 'AU' in between alphabets gr & wacke is misspelled as 'AV'
Wrong Spelling:  gr-av-wacke 
Correct Spelling:  gr-au-wacke 
Explore spell check of Grauwacke to spell without errors.

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