Website:
http://formontana.net/slag.html (Website)

Description:
When copper was smelted, it left behind a byproduct called slag. The smelter in Anaconda was designed to extract copper from the ores mined in Butte. The texture of Anaconda's slag is like sand because the molten slag was spilled into water, causing it to harden and shatter into sand-sized pieces. In fact Anaconda's slag has been used in sand traps at the famous Old Works Golf Course.