Historical clue formulations

• Eponymous mineralogist Friedrich — 2023-09-03
• ___ scale (measure of hardness) — 2023-07-10
• Mineralogical eponym — 2020-09-03
• ___ scale (rater of mineral hardness) — 2020-08-10
• Eponymous scale inventor — 2019-01-15
• ___ scale — 2017-08-18
• ___ scale (measure of hardness) — 2016-10-04
• Inventor of a mineral hardness scale — 2015-09-18
• ___ scale — 2014-10-03
• Mineralogist for whom a scale is named — 2014-09-30
• Kind of scale of mineral hardness — 2012-12-10
• ___ scale — 2011-02-22
• Hardness scale inventor — 2010-04-11
• Eponymous scale developer — 2010-03-04
• ___ scale — 2009-12-27
• ___ scale — 2009-09-23
• ___ scale — 2006-10-08
• Mineralogist Friedrich — 2006-04-20
• Mineral hardness scale inventor — 2004-07-22
• Scale of mineral hardness — 2004-03-09
• Eponymous German mineralogist — 2003-09-20
• Kind of scale — 2003-08-13
• ___ scale — 2002-02-07
• Kind of scale — 2001-04-06
• ___ scale — 1999-03-13
• _____ scale (hardness measure) — 1995-05-03