In reply to Sharon Owen.

The Rolex Lady-Datejust ref. 69173 is equipped with a sapphire crystal. The previous generation (ref. 6917) featured an acrylic crystal; however your watch should have a scratch-resistant sapphire crystal with a cyclops magnification lens over the date.
To answer your other question, it is not advised to ever replace the crystals on Rolex watches with different styles than were originally designed for them. Even when they have the same diameters, other measurements of the crystal differ and the adjacent components (including the bezel that holds the crystal onto the watch) are designed slightly differently for models that are fitted with acrylic vs. sapphire crystals, and this will ultimately cause issues for the watch.