Gemstones: Your Guide to Precious Stones

What are precious stones?

A gemstone is a mineral, rock or organic material that, after being cut and polished, is used in jewellery or as a ornamental, is used in jewellery or as ornamentation because of its beauty, durability and rarity.

Precious stones are highly valued for their aesthetic qualities and because they are often rare and difficult to find.

Distinguishing between precious and semi-precious stones

The distinction between precious and semi-precious stones has never been scientifically valid.

Today, all stones – whether minerals or rocks – valued for their beauty, durability and rarity should be called gemstones.

To understand this change, you need to know a little about the history of gems.

The term precious gemstone used to be applied only to diamonds, emeralds, rubies and sapphires, known as cardinal gems because they had ecclesiastical, devotional or ceremonial uses. The others were called semiprecious.

However, this term is controversial and confusing, as well as devaluing gemstones such as opal, aquamarine, chrysoberyl, amethyst or alexandrite, among other Brazilian stones of great beauty.

Therefore, the distinction between precious and semi-precious stones should be avoided and the term gem should be used instead.

Main characteristics of gemstones

Precious stones are rare minerals valued for their beauty, durability and rarity. Each type has unique characteristics that make it desirable.

1. Diamond

  • Chemical composition: Pure carbon (C)
  • Hardness: 10 on the Mohs scale
  • Colour: Transparent, with possible shades of yellow, blue, green, pink, brown
  • Luster: Adamantine
  • main use: Luxury jewellery, particularly engagement and wedding rings.

2. Sapphire

  • Chemical composition: Aluminium oxide (Al₂O₃)
  • Hardness: 9
  • Colour: Blue (mainly) but also other colours except red (classified as ruby)
  • Luster: Vitreous
  • Main use: Rings, necklaces, bracelets

3. Ruby

  • Chemical composition: Aluminium oxide with chromium
  • Hardness: 9
  • Colours: Red, from light pink to blood red
  • Shine: Vitreous
  • Main use: Rings, earrings, necklaces

4. Emerald

  • Chemical composition: Beryllium aluminium silicate
  • Hardness: 7.5-8
  • Colour: Light to dark green
  • Luster: Vitreous
  • Main use: Rings, necklaces, diadems

5. Amethyst

  • Chemical composition: Silicon dioxide (SiO₂)
  • Hardness: 7
  • Colour: Light to dark purple
  • Shiny: Vitreous
  • Main use: Jewellery, Decoration, Therapy

6. Topaz

  • Chemical composition: Aluminium silicate and fluorine
  • Hardness: 8
  • Colours: Clear, Blue, Yellow, Brown, Green, Red
  • Shine: Vitreous
  • Main use: Miscellaneous jewellery

7. Tourmaline

  • Chemical composition: Aluminium complex borosilicate
  • Hardness: 7-7.5
  • Colours: Green, Blue, Pink, Black, Multicoloured
  • Shiny: Vitreous
  • Main use: Jewellery and collections

8. Opal

  • Chemical composition: Hydrated silica
  • Hardness: 5.5-6.5
  • Colour: Multicoloured with opalescence
  • Luster: Glassy to opalescent
  • main use: Rings, necklaces, earrings

9. Aquamarine

  • Chemical composition: beryllium aluminium silicate
  • Hardness: 7.5-8
  • Colour: Light blue to blue green
  • Shiny: Vitreous
  • Main use: Fine rings and necklaces

10. Citrine

  • Chemical Composition: Silicon Dioxide
  • Hardness: 7
  • Colour: Yellow to yellow-brown
  • Luster: Vitreous
  • Main use: Jewellery and decorative articles

General characteristics of gemstones

  • Hardness: Measured on the Mohs scale, this indicates resistance to scratching.
  • Luster: Reflects the way the light hits it. It can be adamantine, glassy, pearly, etc.
  • Transparency: From transparent to opaque.
  • Colour: One of the main characteristics.
  • Clarity: Refers to inclusions or internal defects.
  • Cut: Influences the brilliance and value of the gem.
  • Rarity: The rarer, the more valuable.

Most admired gemstones in Brazil

1. Amethyst

This is the most sought-after of the Brazilian quartzes, with a purple to violet colour. Discovered in the 19th century, it has made Brazil one of the largest exporters.

2. Aquamarine

From the beryl family, it resembles the blue of the sea. About 90 per cent of the world’s production comes from Brazil. It is also found in Russia, the USA, Afghanistan, Pakistan and India.

3. Citrine

A variety of yellow quartz with iron impurities. Produced with high quality in Brazil, with colours ranging from yellow to intense orange.

4. Emerald

From the beryl family, it is one of the most precious gemstones in the world. Its colour varies from medium to dark green. In Brazil it is found in Goiás, Bahia and Minas Gerais.

5. Imperial Topaz

Brazil is the world’s main source, especially in Ouro Preto (MG). It occurs in rare colours such as cherry red and pink.

6. Paraíba Tourmaline

Extremely rare and with shades of turquoise blue due to traces of copper. Discovered in Paraíba, it has become coveted by brands such as Tiffany and Dior.

7. Rubellite

A variety of tourmaline with shades ranging from pink to bright red. Its name comes from the Latin rubellus (“reddish”). The more intense the colour, the higher its value.