I admittedly responded without reading the source, so please accept my apologies.
Despite how it is worded the total dispersion of Fluorite is less than glass.
That quote is referring to the ‘extraordinary partial dispersion’ property. They are using this to better correct the aberration than could be done with two pieces of glass alone. This seems to be illustrated in the diagrams well.
Some further stuff to read up on is the Abbe number that describes the refractive index vs wavelength derived from a set of light sources.
Despite how it is worded the total dispersion of Fluorite is less than glass.
That quote is referring to the ‘extraordinary partial dispersion’ property. They are using this to better correct the aberration than could be done with two pieces of glass alone. This seems to be illustrated in the diagrams well.
Some further stuff to read up on is the Abbe number that describes the refractive index vs wavelength derived from a set of light sources.
https://en.wikipedia.org/wiki/Abbe_number
The higher the Abbe number the lower the dispersion of a material.
Fluorite is ~95
https://refractiveindex.info/?shelf=main&book=CaF2&page=Mali...
Random choice below but glass tends to be ~25 - 80
https://refractiveindex.info/?shelf=glass&book=HOYA-C&page=E...