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Alta slate is actually called Alta quartzite and is quarried from the mountains around the Alta fjord in Western Europe's greatest occurence of slate. The mountains are owned by the country of Norway. The slate is approximately 700 million years old, containing no fossils- the oldest fossils are 350 million years old. Alta slate, or rather "Alta Quartzite" is seen petrographically not slate, but a mica quartzite in plate-form, so as shale mined in slabs. The rock is extremely hard, so very durable and absolutely freezeproof.
Quartzite is created through metamorphosis mostly of sandstone, but also chert radiolarites or chert are possible as a source rock. Through a combination of pressure, temperature and mechanical stress, the individual quartz grains are deformed in the process by pressure solution, and its crystal lattice begins to re-organize. In this recrystallization then they grow on their original grain boundaries and form a tightly crosslinked structure. The original pore spaces and the sediment structure, depending on the degree of metamorphism, almost completely disappeared. Through an aligned direction of pressure creates the layered structure, which can be split. The origins of rock existing organic components (carbonaceous shares) will be converted into graphite, among other things. The other existing parts of inorganic substance fossils are "degraded" and are no longer available in real quartzites. Accordingly geological research the quartzitic metamorphosis begins in a burial depth of 600 meters and at about 200 ° C.
Besides the color, the cleavage is an important distinguishing feature of quartzite variants. Quartzite block, as it is mined as near Wasa (Sweden), or the blue Azul Macaubas from Brazil is difficult to split. Fissile quartzites usually arise by regional metamorphism: orthogonal to the direction of printing form mica pretending behind a thin separation layers the cleavage direction, a process as it runs similar to the formation of slate. The deposition direction is relevant to the cleavage direction and usability, the frost resistance is not affected.
Alta quartzite (also called Polar-quartzite or North-quartzite) is a metamorphic rock, a stone conversion. Alta quartzite is one of the micaceous quartzite. It was formed in the proterozoic.
This rock came from a quartz-rich clayey sandstone, which is transformed by heat and pressure to form a quartzite, with very different performance characteristics.
Contained in the source rock clay minerals were transformed into white mica (muscovite) by using heat and pressure, which is located on the joint surfaces. The minerals chlorite and sericite-quartz gave it a specific color.
The Slate mining operation started around 1850 and has since been the largest and most stable industry in Alta until today. Alta slate is sought after and exported to the entire world. The extraction of slate rock takes place in four different quarries at "Peska", a mountain made of slate rock, one of many around Alta. The slate is dug out at the slate quarries and processed by the slate factory in Bossekop before being exported to the continent. Alta slate is renowned for being extremley hard and durable and is widely used as roofing tiles and floor covering, so it's used in the UN-building in New York and at the airport in Tokyo.
You'll find an information-panel where you can gather more informations about Alta Slate and your answers for the first two questions, for the 3rd you'll have to look around:
1. When did the slate mining company begin to sell slates to Hammerfest?
2. What kind of ore has been mined around Alta also? (same information-plate)
3. Around the "Nordlysbyen"-monument you can find plates of Alta slate. Get down on your knees and have a look on the plates. What colours characterize the Alta Slate? What colour is the special shimmer?
Send me your answers by mail.