An extract on #sonya6300
The Mohs scale of mineral hardness is based on the ability of one natural sample of mineral to scratch another mineral visibly. The samples of matter used by Mohs are all different minerals. Minerals are pure substances found in nature. Rocks are made up of one or more minerals. As the hardest known naturally occurring substance when the scale was designed, diamonds are at the top of the scale. The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, and/or the softest material that can scratch the given material. For example, if some material is scratched by apatite but not by fluorite, its hardness on the Mohs scale would fall between 4 and 5. "Scratching" a material for the purposes of the Mohs scale means creating non-elastic dislocations visible to the naked eye. Frequently, materials that are lower on the Mohs scale can create microscopic, non-elastic dislocations on materials that have a higher Mohs number. While these microscopic dislocations are permanent and sometimes detrimental to the harder material's structural integrity, they are not considered "scratches" for the determination of a Mohs scale number.
The Mohs scale is a purely ordinal scale. For example, corundum (9) is twice as hard as topaz (8), but diamond (10) is four times as hard as corundum. The table below shows the comparison with the absolute hardness measured by a sclerometer, with pictorial examples.
On the Mohs scale, a streak plate (unglazed porcelain) has a hardness of 7.0. Using these ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale.
Manama has a recently reformed comprehensive bus service that launched on 1 April 2015, with a fleet of 141 MAN buses. Regulated by the Ministry of Transportation, bus routes extend across Bahrain and around Manama with fares of a minimum 200 Fils (BD0.200) (around $0.50(USD); 0.30).
The race directors retain the absolute discretion to exclude any horse from the race, or exempt any horse from the ballot on the race, but in order to reduce the field to the safety limit of 24, horses are balloted out based on a number of factors which include:
prize money earned in the previous two years,
wins or placings in certain lead-up races
allocated handicap weight
The winner of the following races are exempt from any ballot:
Lexus Stakes (formerly Saab Quality and registered as The Hotham Handicap)
LKS Mackinnon Stakes
The Bart Cummings (from 2015)
Doncaster Cup (UK)
Irish St. Leger (IRE)
Tenno Sho (Spring) (JPN)
Sankei Sho All Comers (JPN)
Arlington Million (USA)
San Juan Capistrano Handicap (USA)
Australian Stayers Challenge
The limitation of 24 starters is stated explicitly to be for safety reasons. However, in the past far larger numbers were allowed - the largest field ever raced was 39 runners in 1890.