text: one way to help identify a mineral is to rub it against a piece of porcelain tile. this procedure tests the __ a.streak b.hardness c.luster d.cleavage  and another question...?  which one of the following statements represents a qualitative observation?  a.the stratosphere begins 40 kilometers above the surface of earth.  b.the circumference of earth is 40,074 kilometers.  c. the sun is larger than earth.  d. the distance between two lines of latitude is approximately 112 kilometers. scraping a mineral sample on a porcelain plate is used to test the streak of the material.  some minerals leave a streak of a different colour than you might expect from the colour of the sample itself.  for example, many iron compounds are greyish/steely in colour, but leave a reddish streak.  this can be used as an identifying characteristic.  the porcelain plate can also be used as part of a hardness test, in that a very hard mineral (i.e. diamond) would scratch the plate without really leaving a streak.  as far as the second question:  c - it describes a quality (the relative size of the sun and earth), but not a quantity (as the others do), thus it is a qualitative statement.