Wedge/spacer materials

Hello folks,

Im getting all geared up to do several restorations.

So far I have:
4 very nicely patterned woods that I can use
Pins and washers etc
Polished blades ready for the scales.

What I dont have is a suitable material for the wedge/spacer.

I have seen people use stone for a spacer and I liked the look of it.

Working the stone is not an issue as I have access to lapidary equipment (and some experience)

The woods range from a deep red (jarrah) to a mudy blonde burl (ironwood burl).

I've looks at some lapis lazuli and some green agate but would like the opinions of others as to workability and colour combinations.

Cheers Guys