The estimated value of nonfuel mineral production for Wyoming in 2001 was nearly $986 million, an increase of about 1% over 2000. According to preliminary figures, in 2001 Wyoming produced 3.16 million metric tons of bentonite, worth $131 million, as well as 5 million metric tons of crushed stone, valued at $21.5 million. No metal production has been reported since 1984. Wyoming ranked 15th nationally in the value of nonfuel mineral production. Wyoming continued to rank 1st in the nation in bentonite production. In 2001, major uses of Wyoming bentonite were as pet waste absorbent, drilling mud, pelletizing iron ore, in foundry sand, and as a waterproof sealant. Wyoming also continued to lead the nation in soda ash production from the world's largest known resource of trona, a natural sodium carbonate-bicarbonate. Trona mined in Wyoming was used to produce soda ash, caustic soda, sodium sulfite, sodium bicarbonate, sodium cyanide, and calcined trona. Grade-A helium production increased slightly; of the four states that produced grade-A helium, Wyoming ranked 2nd. The combined value of portland cement, common clays, crude gypsum, grade-A helium, lime, and soda ash in 2001 was $809 million.