Search results show that this material is:
Extremely rare, mined out in the 1970s near Winslow, Arizona
Colored green due to ~2% chromium in the chalcedony replacement
Highly desired by collectors because the deposit is long gone
Known to darken with humidity, which adds to its uniqueness
Small pieces (5–30 grams) sell for $50–$90 on specialty sites.
Medium pieces (50–120 grams) sell for $250–$600+ on eBay