Material
White alley marbles are usually made of white marble or alabaster.
Use
White alley marbles were usually used as "shooters", or for shooting at other marbles.
Value
White alley marbles were prized more highly than most other marbles, especially "commoneys" or marbles made of clay or plaster. ̶0;The Playground, or Out-Door Games for Boys, A Book of Healthy Recreations for Youth,̶1; a book published in 1866, suggests a white alley would be worth four commoneys.
Name
"Alley" is short for "alley-tor". "Tor" is Celtic for "rock" or "stone", and some suggest that "alley" is a reference to alabaster.
Superstition
A white alley was considered lucky, as it was highly prized and much envied.