Hello boris64,
Parakeet is a collectors name given to smaller sized "Parrots". Parrot is actually a Vitro Name.
I copied and pasted some info from this website
https://www.marblecollecting.com/marble-reference/online-marble-id-guide/vitro-agate-co/
Vitro Agate also produced another type of brushed opaque marble called the “Parrot” that is collectible. This is a white base marble that has four patches of color on it. The patches can be blue, purple, black, yellow, and green (aventurine or not).
"Parakeets" are 5/8” to 11/16” varieties of Parrots.
Hope this helps,
Marble--On!!