"rob it of a few petrified spars"
Moss Rake, England (where Derbyshire spar is now quarried)
Creative Commons Attribution Share AlikeMoss Rake, England (where Derbyshire spar is now quarried) - Credit: Dave Dunford, Geograph Project
A spar is a lightly coloured crystal which naturally occurs in geometrical, smooth-sided shapes.

Derbyshire spars are mostly calcite, though Derbyshire Blue John or fluorite was also appreciated for its colour.

 

Calcite from England
GNU Free Documentation LicenseCalcite from England - Credit: Ra'ike, Wikipedia Commons