MH: Inorganic, Micaeceous or Diatomaceous Elastic Silts

What does MH mean? The above is one of MH meanings. It may have other definitions. Please refer to the end of this passage.

MH: Inorganic, Micaeceous or Diatomaceous Elastic Silts

Definition in English: Inorganic, Micaeceous or Diatomaceous Elastic Silts