Instrument data from three buoys in Lake Superior provide a reliable record of water temperatures since about 1980, and the information also shows that, with water temperatures running in the mid-to-upper 60s (and even warmer closer to shore), âwe are at record temperatures for this time of year,â according to Austin.
The talc is formed by the alteration of sedimentary magnesium carbonate rocks (dolomite and magnesite) at elevated temperature and pressure below the earth's surface. While the magnesium is fixed in situ, the silica is transported by silica-containing hot fluids to react with the Magnesium- bearing carbonates to form talc. These altered rocks are then talc-rich dolomites or magnesites. This type of deposits usually deliver the massive talcs accompanied by carbonates, chlorite and some quartz.
Talc has a specific gravity of 2.5â2.8, a clear or dusty luster, and is translucent to opaque. Talc is not soluble in water, but is slightly soluble in dilute mineral acids. [citation needed] Its colour ranges from white to grey or green and it has a distinctly greasy feel. Its streak is white.