Three quarries were operational by the end of 1938, and a fourth opened in April 1941. All four quarries were located near the main camp, and the total planned output was annually. The stone was average quality blue-gray and yellow-gray granite, 90% of which was suitable for architectural purposes. Production gradually increased during 1940, but remained constant in 1941. Initially all work was done by manual labor; prisoners worked alongside civilian laborers and performed the most arduous and dangerous tasks. Accidents led to many deaths. Beginning in 1940 and 1941, machines were introduced to increase efficiency. In mid-1939, the quarries became the main use of labor in the camp and the following year they consumed half of the total labor, which was valued at 367,000 Reichmarks.