You might try a couple of books that I have found useful when
researchingsome history of gems and jewelry. One is:
Jewelry 7,000 years by Hugh Tait, published by Hary N. Abrams
1986 the other is:
Gems by Mab Wilson, published by William Heinemann Ltd, London,
I haven’t checked on Spectrolite from Finland, but they do have
alot of historical info on alot of stones and jewelry.