Tarquin 'Unusual Artefact' as bonus...what is it?

[CircleC]

I found the Anathema half in the Surrey crypt and gave it to Tarquin. In the dialogue I asked for more than thanks and he gave us a sword called 'Unusual Artefact'. 1 pound, 0 gold, no stats, 'An odd, crystalline (and, apparently, sentient) object pulsating with eldritch energy.' Cannot be sold, equipped or combined. When used, the narrator says, 'The crystalline artefact is both beautiful and robust; as pure as glass, and as immutable as iron.' It displays a single option: '1. Return the object to your pack'. Is this just a paper-weight? Or does it have some role?

[Xaphnir]

Find the second half.

[Chaoslink]

Yeah, I don't think he actually takes it from you until you have all the parts.

[CircleC]

Ah. Must be. Thanks