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.
Best Answer
A non-magical crystal ball is sufficient
assuming it is worth at least 1000 gp. We can see this from the typography of the spell listing, in which the words "crystal ball" are not italicized. The D&D 5e rulebooks consistently italicize the names of magic items anywhere they are used (except section headings), as per the D&D Style Guide.
It also makes sense from a design intent perspective: why list a crystal ball as a possible component if you could cast the spell directly from the magic item anyway?