Mendip Hills In some areas the limestone and the dolomitic conglomerate have been mineralised with lead and zinc ores. From the time of Roman Britain until 1908, the hills were an important source of lead. These areas were the centre of a major mining industry in the past and this is reflected in areas of contaminated rough ground known locally as "gruffy". The word "gruffy" is thought to derive from the grooves that were formed where the lead ore was extracted from veins near the surface. Other commodities obtained included calamine (zinc ore), manganese, iron, copper and baryte. The eastern area reaches
Group 5 element magnesium. 230,000 metric tons of niobium ore are produced yearly, with Brazil producing metric 210,000 tons, Canada producing 10000 metric tons, and Australia producing 1000 metric tons. 60000 metric tons of pure niobium are produced each year. 70000 metric tons of tantalum ore are produced yearly. Brazil produces 90% of tantalum ore, with Canada, Australia, China, and Rwanda also producing the element. The demand for tantalum is around 1200 metric tons per year. Dubnium is produced synthetically by bombarding actinides with lighter elements. Vanadium's main application is in alloys, such as vanadium steel. Vanadium alloys are used in springs, tools,