DSAE test file

blue ground, noun phrase

Origin:
See quotation 1920.
Geology, Diamond-mining
Eruptive diamondiferous rock which occurs in vertical cylindrical pipes (see pipe), often having a diameter of several hundred feet, and of unknown depth; blue noun sense 1; kimberlite. See also griquaite, hardebank.
Note:
Blue ground is more compacted and often darker in colour than the looser, weathered layers of yellow ground (see yellow sense b) above it.
1882 C. Du Val With Show through Sn Afr. I. 82Digging, delving, and filling up with the precious ‘blue ground’ huge iron buckets.
1985 A.J.A. Janse in Glover & Harris Kimberlite Occurrence & Origin 23When diggers found that much harder compact blue ground underlay the yellow ground, many sold out because they thought that they had reached the bottom of the depression and thus the end of the diamondiferous ground.
Eruptive diamondiferous rock which occurs in vertical cylindrical pipes (see pipe), often having a diameter of several hundred feet, and of unknown depth; bluenoun1; kimberlite.

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18821985