The Scrying spell has as its material component
A focus worth at least 1,000 gp, such as a crystal ball, a silver mirror, or a font filled with holy water
The magic item crystal ball says
While touching it, you can cast the Scrying spell (save DC 17) with it.
If using the magic crystal ball to cast scrying, you would not need to use the crystal ball itself as the focus and material component for the spell it allows you to cast, per DMG p. 141:
Some magic items allow the user to cast a spell from the item. The spell is cast at the lowest possible spell level, doesn’t expend any of the user’s spell slots, and requires no components, unless the item’s description says otherwise.
But suppose you actually knew the spell and could cast it yourself. If you did not have a silver mirror or holy water font, could you use a non-magic crystal ball as a material component?
That is, is the spell specifically asking for the magic item crystal ball, or is a non-magic ball of crystal, provided it is worth 1000gp, sufficient?
For reference, on the PHB adventuring gear list, an arcane focus "crystal" is worth 10gp, while an orb (with the same weight of the magic item crystal ball) is worth 20gp.