Alpine crystals have been studied and collected for hundreds of years, and began to be classified in <answer>the 18th century</answer>. Leonhard Euler studied the shapes of crystals, and by the 19th century crystal hunting was common in Alpine regions. David Friedrich Wiser amassed a collection of 8000 crystals that he studied and documented. In the 20th century Robert Parker wrote a well-known work about the rock crystals of the Swiss Alps; at the same period a commission was established to control and standardize the naming of Alpine minerals.
When did the alpine crystals begin to be classified? 
the 18th century