Quartz Vein Containing Wolframite (Black) (IMAGE) University of Exeter Caption Quartz vein containing wolframite (black) - this is the most important tungsten-bearing mineral in SW England Credit University of Exeter Usage Restrictions Credit: University of Exeter License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.