A light moss green. Most likely a chalcedony with some magnesium in it for the coloring. Lots of stones will strike a spark when struck with iron. The spark occurs typically because a small fragment of iron is scraped from the surface of the steel; because it occurs so rapidly the heat from that friction as well as oxygen in the air cause the iron to ignite or "spark". Small amounts of magnesium, sulfur, iron and oxygen rich silicates can create an enhanced spark as well.
Cherts and flints, same family, are well known for this and are forms of chalcedony.