PINK CHALCEDONY

A semiprecious variety of quartz (silicon dioxide) and a member of the oxide group. It forms in tiny crystals which are aligned parallel to each other. The presence of tiny impurities of iron oxide in the gaps between crystals gives it a distinctive pink colour. There is a range of semi-precious forms of quartz extending from pure chalcedony (milky white) to carnelian and sard (red or reddish brown). Pink chalcedony lies roughly in the middle of this range. It is a relatively hard mineral (7 on the mohs scale).

It has been used for centuries to make bases for statuettes and handles for utensils such as goblets. It can be cut into cabochons and also used for bracelets, cameos, brooches and necklaces. Since it absorbs liquid readily its colour can be artificially enhanced by dying which may increase its commercial value. It can be imitated by coloured glass.

RHODONITE

A silicate made of manganese with silicon and oxygen. It is usually pink or red rose in colour due to its manganese content but may also have black or brown veins. These veins are the result of the various impurities present within the gemstone such as pyrolusite (an oxide of manganese) and will make a specimen much more sought after thus increasing its value. It was first identified in 1819 and takes its name from the Greek word rhodon meaning rose. It sometimes forms in crystals but mostly in great lumps (massive formations). It is moderately hard (5.5-6.5 on the mohs scale) but melts easily. Melting results in the gemstone taking on a glassy appearance. Sometimes crystals are transparent although these are very rare and fragile. Pure samples may be consistent in colour throughout the gemstone but these are also rare. The colour of rhodonite gemstones can change depending on the angle from which they are viewed (a characteristic known as pleochroism).

Most ornaments and jewels are carved from massive formations. It can be used for cabochons, carvings, cameos and beads. Due to its unique appearance it is never artificially simulated. The closest gemstone to rhodonite is rhodochorite but this is softer and susceptible to attack by hydrochloric acid. A genuine rhodonite specimen will not be damaged because rhodonite is insoluble in acid. When freshly extracted from the earth if the surface is slightly discolooured by black marks these impurities can be removed by dabbing with dilute hydrochloric acid.

It is a member of the pyroxenoid group of silicates which are a small offshoot of the pyroxene group. These are minerals with the general formula X2Si2O6 in which x can be aluminium, calcium, iron, lithium, magnesium, sodium or titanium, Other examples include augite, diopside, jadeite and spodumene. Rhodonite is slightly different in that it contains manganese instead of any of the elements listed. Therefore it is known as a pyroxenoid.

It occurs in manganese bearing rocks which have been altered by heat and water millions of years ago (metamorphic). These rocks include various marbles and skarns. Rhodonite has been found at Broken Hill, Australia, Brazil, Canada, Italy, India, Madagascar, New Zealand and Tanzania.