Gemstone characteristics

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

Gemstones are highly valued for their aesthetic characteristics and because they are often rare and difficult to find.

Distinction between precious and semi-precious stones

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

Today, all stones, both minerals and rocks, appreciated for their beauty, durability and rarity, should be called gems.

To understand how this change came about, it is necessary to know a little about the history of gems.

The name precious stone was only used for diamonds, emeralds, rubies and sapphires, known as cardinal gems, because they had ecclesiastical, devotional or ceremonial uses; the other gems were called semi-precious.

However, this term is debatable and confusing, and devalues gems 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 by using the term gem.

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

Main characteristics of gemstones

1. Diamond

  • Chemical composition: Pure carbon (C).
  • Hardness: 10 on the Mohs scale (the hardest of all natural substances).
  • Colours: Transparent, but can have shades of yellow, blue, green, pink, brown and others.
  • Gloss: Adamantine, highly reflective.
  • Main Use: Luxury jewellery, especially engagement and wedding rings.

2. Safira

  • Chemical Composition: Aluminium oxide (Al₂O₃).
  • Hardness: 9 on the Mohs scale.
  • Colours: Mostly blue, but can be found in almost every colour except red (which is classified as ruby).
  • Brightness: Vitreous.
  • Main Use: Rings, necklaces, bracelets and other jewellery accessories.

3. Rubi

  • Chemical Composition: Aluminium oxide with chromium (Al₂O₃).
  • Hardness: 9 on the Mohs scale.
  • Colours: Red, ranging from light pink to blood red.
  • Brightness: Vitreous.
  • Main Use: Fine jewellery, including rings, earrings and necklaces.

4. Emerald

  • Chemical composition: Beryllium aluminium silicate (Be₃Al₂(SiO₃)₆).
  • Hardness: 7.5-8 on the Mohs scale.
  • Colours: Green, ranging from light to dark green.
  • Brightness: Vitreous.
  • Main Use: Sophisticated jewellery, such as rings, necklaces and tiaras.

5. Amethyst

  • Chemical composition: Silicon dioxide (SiO₂).
  • Hardness: 7 on the Mohs scale.
  • Colours: Purple, ranging from light to dark.
  • Brightness: Vitreous.
  • Main Use: Jewellery, decorative pieces and crystal therapy.

6. Topaz

  • Chemical Composition: Aluminium fluoride silicate (Al₂SiO₄(F,OH)₂).
  • Hardness: 8 on the Mohs scale.
  • Colours: Colourless, blue, yellow, brown, green, red.
  • Brightness: Vitreous.
  • Main Use: Rings, necklaces and pieces of jewellery.

7. Turmaline

  • Chemical Composition: Aluminium borosilicate complex (with variables of iron, magnesium, etc.).
  • Hardness: 7-7.5 on the Mohs scale.
  • Colours: Varied (green, blue, red, pink, black, multicoloured).
  • Gloss: Vitreous.
  • Main Use: Jewellery and collectibles.

8. Opal

  • Chemical composition: Hydrated silicon dioxide (SiO₂-nH₂O).
  • Hardness: 5.5-6.5 on the Mohs scale.
  • Colours: Multicoloured with play of colours (opalescence).
  • Brightness: Vitreous to opalescent.
  • Main Use: Rings, necklaces, earrings and pieces of jewellery.

9. Aquamarine

  • Chemical composition: Beryllium aluminium silicate (Be₃Al₂(SiO₃)₆).
  • Hardness: 7.5-8 on the Mohs scale.
  • Colours: Light blue to blue-green.
  • Brightness: Vitreous.
  • Main Use: Fine jewellery, especially rings and necklaces.

10. Citrine

  • Chemical composition: Silicon dioxide (SiO₂).
  • Hardness: 7 on the Mohs scale.
  • Colours: Yellow to yellowish brown.
  • Brightness: Vitreous.
  • Main Use: Jewellery, talismans and decorative objects.

General Characteristics of Precious Stones

  1. Hardness: Measured by the Mohs scale, it indicates resistance to scratching. Diamonds are the hardest.
  2. Brightness: The way light reflects off the surface of the stone. It can be adamantine, vitreous, pearly, among others.
  3. Transparency: It can vary from transparent to opaque.
  4. Colour: Colour is one of the most important characteristics and can vary widely between different stones.
  5. Clarity: This refers to the presence of inclusions or imperfections within the stone. Clearer stones without inclusions are more valued.
  6. Cut: The way the stone is cut influences its brilliance and value.
  7. Rarity: Rarer stones are generally more valuable.


Each gemstone has a unique set of characteristics that make it special and valuable.

The choice of a gemstone for jewellery or personal collections often depends on individual taste, cultural significance and market value. Gemstones are not only objects of beauty, but also have historical, cultural and economic importance.

Features of the most admired gemstones in Brazil

1. Amethyst

Known as the most coveted Brazilian gemstone among quartzes, Amethyst has a colour that varies between purple and violet, transparent to semi-transparent.

Deposits of this popular purple stone were found in Brazil in the 19th century and since then the country has become one of the world’s largest exporters of this marvel.

2. Aquamarine

You’ll probably see the Aquamarine on any list of Brazilian gemstones.

This gem is from the beryl family and got its name from its colour, which is very reminiscent of seawater. This stone varies in both its shade of blue and its size.

Among Brazilian gemstones, this is the most typical. Currently, around 90 per cent of the world’s aquamarine is mined in Brazil. It can also be found in countries such as Russia, the United States, Afghanistan, Pakistan and India.

3. Citrine

Citrine, also called citrine quartz, is a variety of quartz with a yellow, orange and exceptionally red colour. Basically, it is quartz with iron impurities.

Although many Latin American countries are important sources of citrine, such as Argentina, Bolivia and Uruguay, for example, we must emphasise that our country produces some of the best citrine in the world. A member of the quartz family, Brazilian citrine is well known for its warm and unique colours, which usually range from yellow to orange.

4. Emerald

The emerald is one of the most desirable Brazilian gemstones in the beryl metal family. It’s worth noting that its price is one of the highest in the world.

It is said that the first appearances of the emerald date back to Ancient Egypt, but it was considered rare until the Renaissance. According to the ancient Greeks, it is ‘the goddess of all stones’. Its colour, so popularly known, varies from medium to dark green.

The emerald is usually found in Colombia, but it is also present in other countries such as Zimbabwe, Tanzania and Zambia.

In Brazil, the stone is found mainly in Goiás, Bahia and Minas Gerais.

5. Imperial topaz

Brazil is the largest source of Imperial Topaz in the world. Other smaller deposits can be found in countries like Russia, but this is where the largest quantity comes from.

Its main mine is located in Ouro Preto, Minas Gerais, and brings together imperial topaz in yellow, orange, pink, lilac and cherry-red colours. It’s worth remembering that some colours of this gem are extremely rare, unlike pink, which is more easily found.

6. Paraíba Tourmaline

Among Brazilian gemstones, the Paraiba tourmaline stands out because of its rarity. Not least because Brazil has a rich variety of tourmalines.

These unique shades of turquoise are derived from microscopic traces of copper.

This very special gem can be found in the north of Paraíba, which in itself justifies its name.

In some cases, the colours in tourmalines are mixed, resulting in bi-coloured or multi-coloured stones. To give you an idea of how successful this stone is, since it was discovered Paraiba tourmaline has become the target of famous international brands such as Tiffany and Dior, for example.

This rarity can also be found in Africa, in countries such as Mozambique and Nigeria. But let’s be clear, Brazil is the birthplace of this marvel.

7. Rubellite

While we’re on the subject of tourmalines, we can’t forget Rubellite, another variety that attracts attention on the international market for its unique colour, which displays different shades from pink to a vivid red.

Its name comes from the Latin ‘rubellus’, which means reddish. Its value is directly linked to the intensity of its red colour.

In other words, the purer and stronger the colour, the more valuable the gem.

In short, many people don’t realise that Brazil is one of the main sources of precious stones in the world, which is why learning about the origin and characteristics of these rarities is so important.