金刚石是自然界最坚硬的物质。

Diamond is the hardest substance in the physical world.

众所周知，钻石是最坚硬的物质。

It is well-know that diamonds are the hardest substance.

你牙齿的珐琅质是你身体中最坚硬的物质。

The enamel in your teeth is the hardest substance in your body.

珐琅有光泽的坚硬物质包覆在牙齿及一些鳞片（圆鳞与盾鳞）表面。这是脊椎动物所产生最坚硬的物质。

Enamel A shiny hard material covering the dentine of teeth and the surface of some scales ( cosmoid and placoid scales).

作为已知的最坚硬的物质第二，它也是第二个最脆弱的。

Being the second hardest substance known, it is also the second most fragile.

尽管钻石是人类迄今所知最坚硬的物质，但是钻石之间会相互划伤。

Although diamonds are the hardest substance known to man, a diamond will scratch another diamond.

而牙齿是人体内最坚硬的物质之一。

Your teeth are one of the hardest substances in your body.

地表面下40英里深，是地球外壳的边缘，此处非常之热，如同火山喷出的岩浆般的物质替代了坚硬的岩石。

Forty miles deep in the earth is the edge of the outer crust of the earth, and there it is so hot that instead of hard rock there is material much like the hot lava that a volcano erupts.