user: Question: Which formula has a refractive index 589.3 at 1.97?
Columns: ['Material', 'Formula', 'Refractive index(es) 589.3nm', "Hardness ( Mohs' scale )", 'Density (g/cm 3 )', 'State of the art']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Diamond', 'C', '2.417', '10', '3.52', '(Natural)']
SQL:

assistant: SELECT "Formula" FROM "Table" WHERE "Refractive index(es) 589.3nm" = '1.97';