Utah turquoise is not turquoise at all. It is variscite. Variscite is hydrated aluminum phosphate, a rare mineral. It tends to be green in color, whereas turquoise tends toward the blue part of the color spectrum.
Variscite was originally discovered in Germany but has been sold in the U.S. as “Utah Turquoise.” This name comes from the fact that much variscite has been mined from the Lucin and Clay Canyon mines in Utah. Neither mine is producing much of this mineral these days. Most variscite now comes from Nevada and typically has black matrix.
Variscite is a beautiful gemstone in its own right. It is unlikely that individuals selling it as turquoise are doing so fraudulently.