How to read material facts
How to read the material facts on each entry: class-level values, sub-grades, hardness versus durability, colour and identity, and related sources.
General notes
These points apply to the material facts on every entry page. Entry pages link here instead of repeating them under each fact.
Class-level values are not measurements of the entry
Where a fact names the class it covers (a whole class, a mineral group or a parent variety), the figure or description is what the cited clause gives for that class. It was not measured on this entry, and it is not a measured value for this variety.
The clause splits the figure further; only the overall figure is shown
Some clauses give an overall figure and then split it further by variety or by test method. Only the overall figure is shown here; see the cited clause for the finer ranges.
High hardness does not mean durable
A high hardness number does not mean the material resists knocks, acids or temperature changes. Where a fact gives hardness without toughness or stability, that one figure cannot tell you how durable the material is, so please do not read the number as advice on everyday wear.
The national standards we cite (GB/T 16553 and others) give a hardness figure for each entry but no figure for toughness or stability, so every hardness taken only from them is in this position.
When a page has no full durability picture
Judging durability needs the material’s own hardness and toughness. Where a page only has a scattered fact, such as how well a treatment holds up, and cannot put together a complete durability picture, please do not read it as advice on everyday wear.
Colour alone does not establish identity or natural origin
Colour alone cannot establish what a material is, or whether it is natural. Under each colour fact we list other materials whose colour descriptions in the cited standard name the same hue: one colour can belong to several materials.
How two sources on one property relate
Where one property has two sources, we note after the pair how they relate: consistent (they say the same thing); complementary, no conflict (each adds what the other leaves out); different scope; different edition or region; or genuine conflict (they disagree, and we list both rather than pick one).