If these are excluded, it is known today that at least 68 separate mineral species occur across the whole range of the Mont Blanc massif. In order to preserve the mineralogical heritage of Mont Blanc, in 2008 the commune of Chamonix banned all mineral-hunting activities and collection of specimens without a prior permit being issued by the mayor's office. Use of explosives, heavy machinery or helicopters for removing material were also banned, and a code of practice put in place which requires an annual declaration of all finds to be made. It also gives a right for the Chamonix crystal museum (Musée des Cristaux) to have first option to acquire specimens of significance for its collections. To further protect the scientific value of material collected, all specimens offered for sale must be labelled with details of where they were found. The crystal museum opened to the public in 2006 and tells the story of the early crystal-hunters (known as ). Many specimens collected from across the massif are displayed there. Climate Located on the watershed between the Rhône and the Po, the Mont Blanc massif is also situated between the two different climatic regions of the northern and western Alps and that of the southern Alps. Climatic conditions on the Mer de Glace are similar to those found on the northern side of the Swiss Alps. The climate of the Mont Blanc massif is cold and temperate (Köppen climate classification Cfb), and is greatly influenced by altitude. The main valley settlements around the perimeter of the massif are at an altitude ranging between . Daytime valley temperatures in July and August may range up to , sometimes reaching . The greatest snowfall occurs between the months of November and April. The best weather for mountaineering or hiking occurs between late June to early October but, being the highest part of the Alps, the Mont Blanc massif can create its own weather patterns. Temperatures drop as the mountains gain in height, and the summit of Mont Blanc is a permanent ice cap, with temperatures around . The summit is also prone to strong winds and sudden weather changes. Because of the massif's great overall height, a considerable proportion is permanently glaciated or snow-covered and is exposed to extremely cold conditions. Even on the high passes of the Tour du Mont Blanc, around , summer temperatures can be between , but feeling