P4: L’Argenteria
Fourth stop
L’Argenteria
Interestingly, these three metals appear together on the periodic table of the elements. They are called minting metals since historically, they were the three metals used for this purpose. There are four reasons why this is the case: they are easily obtained in a metallic state; they are malleable, so they can be made into metal discs with a design; they are slightly chemically reactive; and, in the case of silver and gold, the low abundance of these metals meant that the coins had the intrinsic value of the metal itself.
In addition to metals, there are several different gems that are used in jewelry. A gem is a mineral, rock or petrified material that when cut and polished can be used in jewelry. Some are organic, such as amber (fossilized tree resin). Traditionally, gems were divided into two large groups, precious and semi-precious. Five types of gems were considered precious: diamond, ruby, sapphire, emerald and amethyst. Amethyst is no longer considered precious, since large quantities of it were discovered in Brazil.
- Ruby contains chromium (III) impurities and is red.
- Sapphire contains iron (II and III) and is blue.
- Emerald contains chromium (III) and vanadium (III) and is green.
- And amethyst contains chromium (III) and titanium (IV) and is violet.
The fifth precious gem, diamonds, are the most highly valued. The beauty of their glow is due to the fact that they have a high light refraction index and great power of dispersion: when rays of light enter the crystals, they result in innumerable internal reflections and the white light is dispersed, turning it into a fan of multiple colors. It is similar to what happens with raindrops when they become a rainbow.
Did you know?
Coal burning in stoves has a chemical composition that is very similar to diamonds, i.e., carbon. When coal is burned, the carbon reacts with oxygen in the air, resulting in carbon dioxide, a gas that flows out through the chimney. In addition to carbon, coal also contains small amounts of other molecules that contain elements such as sulfur or nitrogen.
Some of these molecules burn and give off gases, but others result in solids. This residue left after burning coal is what we call ash. If we were to burn diamonds in an oven, there would be no ash.
Taula periòdica
Els elements s’agrupen en la taula periòdica en funció dels electrons que tenen i de la seva distribució, el que s’anomena configuració electrònica. Per un mateix grup, la configuració electrònica coincideix en el nombre d’electrons de la darrera capa, tot i que el nivell energètic que ocupen és diferent.

Corindó
El corindó és un mineral de fórmula Al2O3 que té una gran duresa (valor 9 en l’escala de Mohs, en la qual el diamant té duresa 10 i el quars, 7), elevat punt de fusió, poca reactivitat química i bones propietats com a aïllant elèctric.
Aquestes característiques han permès que el corindó sigui utilitzat com a abrasiu (també en pasta de dents), com a refractari (material resistent a temperatures elevades), i també en ceràmiques. A més, és una de les matèries primeres principals en la obtenció de l’alumini metàl·lic.

Arc de Sant Martí
Els diamants i les gotes d’aigua funcionen com prismes al frenar, en major o en menor grau, les longituds d’ona de la llum. La llum blanca conté tots els colors de l’espectre (del violeta al vermell). La llum quan travessa un prisma es descompon en els seus colors originals, que s’estenen en forma d’arc de Sant Martí.

Plàstics
Els plàstics són materials orgànics, polimèrics, derivats del petroli. Poden tenir origen natural (com el cautxú) tot i que la majoria són sintètics, obtenint així una gran diversitat de plàstics.
Una de les seves principals propietats és que a l’aplicar-li una força pot canviar la seva forma, recuperant-la quan es deixa d’aplicar. Els plàstics presenten baixa densitat, són bons aïllats elèctrics i tèrmics, i capaços de resistir molts factors químics. A més, poden reciclar-se i n’existeixen de biodegradables.
