A form of aluminium oxide, Corundum is a rock-forming mineral that is typically found in metamorphic, igneous, and sedimentary rocks. The mineral is best known for its gem varieties, with the most notable stones being Ruby and Sapphire. Both classified as Corundum, the only difference between Ruby and Sapphire is their colouring. Ruby is the red variety of the mineral, while all other colours are classified as Sapphire. The terms ‘Ruby’ and ‘Sapphire’ are only used to describe the gem variety of the mineral; in all other circumstances, it is simply referred to as Corundum.
In addition to its beautiful gemstones, Corundum is known for its immense hardness. Measuring a 9 on the Mohs scale, the hardness of the stone makes Corundum a popular abrasive. Both natural and synthetic forms of the stone are used in a range of industrial applications; most notably, the material is used to grind optical glass, polish metals, and create industrial bearings. In this article, we explore the mineral in more detail.
There are a number of different ways to identify Corundum. Most commonly, the stone is identified by its extreme hardness. Corundum is the second hardest mineral in the world, with Diamond being the first. In addition to being hard, the stone is also stable. Rarely affected by acids or the environment, the mineral is popular for use in various industrial applications. The most common forms of the stone are Emery and Translucent Brown Corundum; due to their toughness, these forms are typically used as abrasives. As the name suggests, Translucent Brown Corundum can be identified by its colour. Emery is typically black or dark grey in colour. Occasionally, Erosion can cause Emery to turn into a type of sand; black in colour, the distinct material is often referred to as “black sands”.
In its natural state, Corundum is completely transparent. However, the presence of trace impurities gives Corundum a range of different colours. Ruby, a famous gem-variety of Corundum, appears red in colour due to traces of chromium in the stones composition. All other colours of gem-quality Corundum are referred to as Sapphire, with the most famous colour of the stone being blue. Blue stones are blue due to the presence of iron and titanium in their composition. Technically, all gem-quality Corundum specimens are classed as either Ruby or Sapphire; however, the gemstone market has various trade names for different colours of the stone. Below, we explore a few of the most common.
Emery is a common variety of Corundum. With an extreme hardness and abrasive nature, the stone is often used for industrial applications. Emery is black in colour due to the presence of Hematite, Spinel, and Magnetite.
Padparadscha is an orange variety of Sapphire. This type of stone is incredibly rare so carries with it a hefty price tag.
Ruby is a red variety of Corundum. Occasionally, specimens can exhibit a pink tone.
All gem varieties of Corundum can be classed as Sapphire, with the exception of the red stones which are classed as Ruby. In terms of trade names, Sapphire generally refers to blue varieties of the stone, unless a separate colour is mentioned at the beginning of the name; for instance, Pink Sapphire. In the gem trade, Sapphire with a colour other than blue is often referred to as “fancy”.
Red stones that display a six-rayed star, or asterism, are classed as Star Ruby.
Blue stones that display a six-rayed star, or asterism, are classed as Star Sapphire.
Varieties of Corundum are found in various locations worldwide. Typically, the stones are found in sedimentary, igneous, and metamorphic rocks. Notable sources include India, Burma, South Africa, Russia, Sri Lanka, Thailand, Cambodia, Afghanistan, Colombia, Japan, Scotland, Nepal, Tanzania, and Australia.
Often referred to as the stone of wisdom, Corundum is believed to aid decision making. The precious stone is also thought to release tension and ill-thoughts from the mind, making it ideal for those suffering from anxiety and depression. Additionally, the stone soothes the muscles and calms the mind, providing the beholder with a sense of peace and happiness.
As mentioned previously, Corundum gemstones are classed as either Ruby or Sapphire. In terms of crystal healing, Ruby works wonders for recharging your energy levels. The red gem is also thought to stimulate the mind, encouraging self-confidence and positivity. The deep red colour of the stone is thought to be associated with love and sexual energy. With this in mind, Ruby can benefit those suffering from sexual dysfunction. The heart-centred stone is also thought to encourage long-lasting relationships.
Sapphire is best known for releasing mental tension and unwanted thoughts. The beautiful gem restores balance within the body by aligning the physical and emotional planes. Ideal for those suffering from spiritual confusion, Sapphire encourages serenity and peace of mind. Physically, the gemstone is believed to prevent excessive bleeding and strengthen the veins. These properties make the stone ideal for those suffering from blood disorders.
Corundum of all varieties is popular worldwide. Gem-varieties of the stone, such as Ruby and Sapphire, are often used within designer jewellery. Due to its extreme hardness, other forms of Corundum are used within industrial applications; most notably, the mineral is used to grind optical glass, polish metals, and create industrial bearings. Whether you’re looking for a new addition to your jewellery collection or you’re hoping to take advantage of the stones extreme toughness, purchase a good-quality piece of Corundum to reap the benefits.