Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Material | Formula | Refractive index(es) 589.3nm | Hardness ( Mohs' scale ) | Density (g/cm 3 ) | State of the art |
| --- | --- | --- | --- | --- | --- |
| Diamond | C | 2.417 | 10 | 3.52 | (Natural) |
| Artificial Simulants: | Artificial Simulants: | Artificial Simulants: | Artificial Simulants: | Artificial Simulants: | Artificial Simulants: |
| es Glass | Silica with Pb , Al , &/or Tl | ~ 1.6 | < 6 | 2.4 – 4.2 | 1700 – |
| White Sapphire | Al 2 O 3 | 1.762 – 1.770 | 9 | 3.97 | 1900–1947 |
| Spinel | MgO·Al 2 O 3 | 1.727 | 8 | ~ 3.6 | 1920–1947 |
| Rutile | TiO 2 | 2.62 – 2.9 | ~ 6 | 4.25 | 1947–1955 |
| Strontium titanate | SrTiO 3 | 2.41 | 5.5 | 5.13 | 1955–1970 |
| YAG | Y 3 Al 5 O 12 | 1.83 | 8.25 | 4.55 – 4.65 | 1970–1975 |
| GGG | Gd 3 Ga 5 O 12 | 1.97 | 7 | 7.02 | 1973–1975 |
| Cubic Zirconia | ZrO 2 (+ rare earths) | ~ 2.2 | ~ 8.3 | ~ 5.7 | 1976 – |
| Moissanite | SiC | 2.648 – 2.691 | 8.5–9.25 | 3.2 | 1998 – |
| Natural Simulants: | Natural Simulants: | Natural Simulants: | Natural Simulants: | Natural Simulants: | Natural Simulants: |
| Quartz | Silica | 1.543 – 1.554 | 7- | 2.50 – 2.65 | Ancient |
Question:
Which formula has a refractive index 589.3 at 1.97?
Answer:
Gd 3 Ga 5 O 12