▁to ▁the ▁Seven ▁Stars ▁public ▁house ▁in ▁Derby . ▁The ▁plan ▁was ▁to ▁au ction ▁them ▁due ▁to ▁the ▁r ar ity ▁of ▁un work ed ▁Ash ford ▁Black ▁mar ble . ▁It ▁was ▁spec ulated ▁that ▁the ▁rocks ▁had ▁been ▁abandoned ▁when ▁an ▁Ash ford ▁Black ▁Mar ble ▁manufact urer ▁moved ▁in ▁the ▁ 1 8 8 0 s . ▁ ▁Ge ology ▁ ▁Although ▁referred ▁to ▁as ▁mar ble , ▁the ▁rock ▁is ▁of ▁purely ▁sed iment ary ▁origin . ▁It ▁is ▁a ▁dark , ▁fine - gra ined , ▁mud dy ▁Car bon ifer ous ▁lim estone , ▁rich ▁in ▁bit umen ▁which ▁gives ▁it ▁its ▁dark ▁grey ▁colour ation ▁which ▁turns ▁a ▁gl oss y ▁black ▁when ▁pol ished ▁and ▁surface ▁treated . ▁The ▁prime ▁source ▁of ▁this ▁rock ▁was ▁from ▁Ar rock ▁Mine , ▁and ▁later ▁in ▁ 1 8 3 2 ▁from ▁nearby ▁Ro ok ery ▁Plant ation , ▁near ▁Ash ford - in - the - W ater . ▁ ▁Man ufact uring ▁techniques ▁▁ ▁The ▁lim estone ▁can ▁be ▁turned ▁on ▁a ▁lat he ▁to ▁create ▁ur ns , ▁cand l est icks ▁and ▁other ▁similar ▁objects , ▁or ▁sa wn ▁to ▁produce ▁smooth , ▁flat ▁items ▁such ▁as ▁ob el is ks ▁and ▁paper we ights . ▁Derby ▁Museum ▁and ▁Art ▁Gallery ▁holds ▁collections ▁of ▁worked ▁and ▁part - work ed ▁items ▁of ▁Ash ford ▁Black ▁Mar ble , ▁acquired ▁from ▁an ▁in lay ing ▁work shop ▁owned ▁by ▁the ▁Tom lin son ▁family