It is actually white magnesite with brown mottling, just like a paint horse. It also contains hematite.
Though sometimes called White Turquoise or Wild Horse Turquoise-it is not Turquoise.
This semiprecious stone is often used in Native American designs.
Wild Horse was found in the mid-90's near the Globe copper mine in the Gila wilderness area of southeastern Arizona. You can not drive to the location, so all the material has to be hiked out over a mile through rugged terrain.
Wild Horse has a hardness of 4, so care should be taken when setting, polishing and wearing Wild Horse cabochons.
Wild Horse (or Magnesite) is said to be a calming and soothing stone. It is believed to be a powerful emotional balancer. Wild Horse is said to be especially helpful to those under extreme stress and/or who are unable to release control. Wild Horse promotes joy and emotional harmony.