| DIAMOND | Form of pure carbon esteemed as a gem that is the hardest naturally occurring substance (7) |
| GARNET | Derived from Latin meaning "pomegranate", a gem that is the colour of the arils of said fruit (6) |
| ENAMEL | Tissue that is the hardest substance in the human body (6) |
| MINERAL | Broadly, any inorganic naturally-occurring substance that is neither animal nor vegetable (7) |
| EMERALD | Green variety of beryl esteemed as a precious gem (7) |
| ESSENCE | Vanilla -; ingredient used to flavour ice cream, custard and sponge cake; a concentrated form of pure extract (7) |
| FASTONE | Female, a gem that cheat pulls (4,3) |
| ORTOLAN | Old World bunting esteemed as a delicacy |
| FERRITE | Form of pure iron |
| APHID | A black fly, greenfly or other sap-sucking homopteran whose main predator, the ladybird, is duly esteemed as a "gardener's friend" (5) |
| CURLY | - kale; originally grown as cattle fodder, a leafy brassica esteemed as a superfood (5) |
| AMBER | Typically in shades of honey-yellow, golden-brown or cognac, a form of fossilised resin derived from ancient trees which is used as a gem (5) |
| SOFEW | "Thinking is the hardest work there is, which is probably the reason why ___ engage in it": Henry Fo |
| EXPERIENCE | "___ is the hardest kind of teacher. It gives you the test first and the lesson afterward": Oscar Wilde (10) |
| LAMPBLACK | Form of almost pure carbon used as a pigment (9) |
| OPAL | Form of silica, opaque or transparent with an iridescent play of colours valued as a gem |
| SCARAB | Gem that is a horse, perhaps |
| LIE | "Tuesday is the hardest crossword of the week," e.g. |
| MOONSTONE | A gem that shines only at night? |
| CHASTE | Pure carbon as the makeup of it (6) |
