I'm not going to beat this to death but ........
I worked for 32 years in metal fabrication for the marine industry, many of the parts I worked on had been or were going to be hard coat anodized. On average I delivered & picked up well over 10,000 pounds of aluminum a year to/from the anodizer (was ALCOA in Vancouver WA).
Hard coat anodizing is so tuff it dulls drill bit and saw blades and last well for decades. Nothing short of a sharp/pointy object will scratch it and even then it's not easy, rubbing from a boot for a week will not do it.
There are other types of anodizing which produce a much softer less durable finish, but I would not refer to them as "hard"
(Duranodic) anodizing.
"It is an electrochemical process that thickens and toughens the naturally occurring protective oxide. The resulting finish, depending on the process, is the second hardest substance known to man, second only to the diamond."
and
"Hard Anodizing is a term used to describe the production of anodic coatings with film hardness or abrasion as their primary characteristic. They are usually thick by normal anodizing standards (greater than 25 microns) and they are produced using special anodizing conditions (very low temperature, high current density, special electrolytes). They find application in the engineering industry for components which require a very wear resistant surface such as piston, cylinders and hydraulic gear. They are often left unsealed, but may be impregnated with materials such as waxes or silicone fluids to give particular surface properties."
From here:
http://www.anodizing.org/Anodizing/definitions.htmlSorry for the long post.
Bruce