Here is an interesting bit of marble history describing how "agate" marbles were made in Germany, from The Manufacturer and Builder dated December, 1884. Excerpt:
Almost all the "marbles" with which boys everywhere amuse themselves, in season and out of season, on pavements and in shady spots, are made at Oberstein, Germany. There are large agate quarries and mills in that neighborhood, and the refuse is turned to good account in providing the small stone balls for experts to â€œknuckleâ€ with.
You can read the full article here.