The term "scale of hardness" is correct and usable in written English.
It is often used to describe a range of hardness values from one material to another. For example, "The scale of hardness of granite ranges from 6 to 7 on the Mohs scale."
Pencils come in a scale of hardness, from "hard" pencils, like H, to "soft," like 9B.
Widely known as the hardest natural material, they achieve a perfect ten on the Mohs scale of hardness.
It is a property by which minerals may be described relative to a standard scale of 10 minerals known as the Mohs scale of hardness.
This can be done by using the Mohs scale of hardness, which lists 10 common minerals in their relative order of hardness: talc (softest with the scale number 1), gypsum (2), calcite (3), fluorite (4), apatite (5), orthoclase (6), quartz (7), topaz (8), corundum (9), and diamond (10).
Diamond is the hardest known natural material on the Mohs scale of mineral hardness, where hardness is defined as resistance to scratching and is graded between 1 (softest) and 10 (hardest).
Consider Moh's scale of mineral hardness, which assigns mineral $m_1 $a higher score than mineral $m_2 $iff $m_1 $can scratch, but cannot be scratched by, $m_2 $
FA is the hardest (five according to the Mohs' scale of mineral hardness), most stable and least soluble compound among all CaPO4 (Table 1).
Synthetic diamond is the hardest material known, where hardness is defined as resistance to scratching and is graded between 1 (softest) and 10 (hardest) using the Mohs scale of mineral hardness.
Known to the ancient Greeks as ἀδάμας – adámas ("proper", "unalterable", "unbreakable") and sometimes called adamant, diamond is the hardest known naturally occurring material, scoring 10 on the Mohs scale of mineral hardness.
Diamond is the hardest gemstone, ranking a 10 on the Moh's scale of mineral hardness, and sapphire ranks at 9.0 on the same scale.
Back redness (erythema), presence of scales (scaling), and hardness of the skin were scored using a semiquantitative scoring system from 0 to 4 based on their external physical appearance: 0 = no skin abnormalities, 1 = slight, 2 = moderate, 3 = marked, and 4 = severe.
