Sgian Dubh handed down from my girlfriends grandfather

[Dughlas mor]

Same thing, actually, or was at one time. In the gemstone world, Cairngorm was once a term used to designate the dark yellow to dark brown (smoky) quartz that originated in the Cairngorm Mts. I understand that those deposits were used up years ago. The orange to orange reddish stones often seen on antique or vintage dirks and sgians, referred to as Cairngorms are likely amythest that has been heat treated to change the color.