appears to be a Wedgwood Cameo Goblet - issued, apparently, mainly to commemorate special occasions, i.e. royal events, when there would have been a suitable cameo inset in the seal - the cameo itself having a blackish background. Made in three colours - smokey blue, topaz and amethyst. Not used very often for general giftware, apparently, so yours may be less common in fact than those carrying the actual cameo - but that is conjecture only

Certainly produced throughout most of the 1970's, and should be 12.75 cms. tall.
Ref. Wedgwood Glass - Susan Tobin - 2001.