Gemstone Lexicon
Gemstones are fascinating due to their colors, natural structures, and special gemological properties. Our gemstone lexicon provides you with an understandable overview of selected gemstones, their characteristics, typical treatments, as well as notes on care and use in jewelry.
Please note: Natural gemstones are individual natural products. Color, transparency, inclusions, and appearance can vary from stone to stone. The images on this page serve for illustration purposes and do not show specific Sirius Diamant product stones.
Gemstone hardness: What does the Mohs scale mean?
The Mohs scale describes a mineral's resistance to scratching. A higher value indicates greater scratch hardness.
However, hardness alone does not mean that a gemstone is indestructible. Toughness, cleavage, inclusions, treatments, and sensitivity to heat, chemicals, and temperature fluctuations also influence its durability.
Therefore, even a very hard gemstone should be protected from strong impacts and improper handling.
Aquamarine
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Mineral: Beryl
Color: Green-blue to blue
Mohs hardness: 7.5–8
Birthstone: March
What is aquamarine?
Aquamarine is the green-blue to blue variety of the mineral beryl. Emerald also belongs to the same mineral family.
The name is derived from the Latin expression for "seawater" and refers to the gemstone's characteristic color range.
Color and quality
Aquamarines range from very pale blue to slightly greenish blue to more intense shades of blue. Many faceted aquamarines have high transparency and relatively few inclusions visible to the naked eye.
When evaluating them, color, clarity, cut, proportions, and size play a particularly important role.
Treatments
Aquamarine is frequently heat-treated in the gemstone trade to shift greener hues toward a purer blue. Whether a specific stone has been treated always depends on the information provided for the respective gemstone or piece of jewelry.
Care of aquamarine
Due to its hardness, aquamarine is well-suited for jewelry, but should be protected from strong impacts and scratches. Lukewarm water with mild soap is a gentle cleaning method.
Tradition and meaning
Aquamarine is traditionally the birthstone of the month of March. Its sea-like color has historically been frequently associated with water and seafaring.
Amethyst
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Mineral: Quartz
Color: Violet to purple
Mohs hardness: 7
Birthstone: February
What is amethyst?
Amethyst is the violet variety of the mineral quartz. Its color palette ranges from delicate lilac to deep, vibrant purple tones.
Color and quality
An attractive color effect, transparency, and a well-executed cut are particularly important. Natural amethysts can have color zoning of varying intensity.
Treatments
Heat treatments can be used to alter the color or lighten very dark stones. Under certain conditions, heating amethyst can also produce yellow to orange quartz, which is traded as citrine.
Care of amethyst
Clean amethyst preferably with lukewarm water and mild soap. Very high temperatures and intense, prolonged heat should be avoided. Intensive long-term exposure to light can affect the color of some stones.
Tradition and meaning
Amethyst is the traditional birthstone of the month of February and has a long cultural history in both secular and religious jewelry.
Citrine
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Mineral: Quartz
Color: Yellow to orange or brownish-orange
Mohs hardness: 7
Birthstone: November
What is citrine?
Citrine is the yellow to orange variety of quartz and therefore belongs to the same mineral family as amethyst.
Natural and heat-treated citrine
Naturally occurring citrine is relatively rare. A large portion of the citrine offered in the gemstone trade is created through the controlled heat treatment of amethyst.
Color and quality
Citrines are evaluated primarily based on color effect, transparency, cut, and visible inclusions. Color preferences range from bright, sunny yellow to vibrant golden or orange tones.
Care of citrine
Citrine should be protected from scratches, strong impacts, and abrupt temperature changes. Lukewarm water and mild soap are well-suited for cleaning.
Tradition and meaning
Along with topaz, citrine is one of the traditional birthstones of the month of November.
Ruby
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Mineral: Corundum
Color: Red to purple-red
Mohs hardness: 9
Birthstone: July
What is ruby?
Ruby is the red variety of the mineral corundum. Corundum in other colors is generally classified in the sapphire group.
Color, clarity, and inclusions
Color is among the most important quality factors of a ruby. Natural rubies can have visible or microscopic inclusions. The location and characteristics of these features can affect transparency, appearance, and durability.
Treatments
Heat treatments are common for ruby. In addition, other processes such as diffusion treatment or fracture filling exist. Fracture-filled stones, in particular, can be more sensitive to chemicals and intensive cleaning procedures.
Care of ruby
Untreated and exclusively heat-treated rubies are generally very resilient. Lukewarm water with mild soap is a gentle cleaning method.
Tradition and meaning
Ruby is the traditional birthstone of the month of July and has been counted among the most important red jewelry gemstones for centuries.
Sapphire
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Mineral: Corundum
Color: Especially known in blue, as well as numerous other colors
Mohs hardness: 9
Birthstone: September
What is sapphire?
Like ruby, sapphire belongs to the mineral species corundum. While red corundum is referred to as ruby, sapphires can appear in numerous other colors.
Besides blue, there are, among others, pink, yellow, orange, violet, and green so-called fancy sapphires.
Color and quality
In blue sapphires, hue, saturation, and lightness can vary considerably. Transparency, cut, and natural inclusions additionally influence the appearance.
Treatments
Heat treatment is a well-known and common gemstone treatment for sapphire. In addition, there are, for example, diffusion, filling, and dyeing processes.
Care of sapphire
Sapphire has a Mohs hardness of 9 and is well-suited for many types of jewelry. Lukewarm water with mild soap is generally a gentle cleaning method.
Tradition and meaning
Sapphire is the traditional birthstone of the month of September. Historically, blue sapphire has been associated with, among other things, loyalty, sincerity, and dignity.
Emerald
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Mineral: Beryl
Color: Green to bluish-green
Mohs hardness: 7.5–8
Birthstone: May
What is emerald?
Emerald is the green to bluish-green variety of the mineral beryl. Aquamarine belongs to the same mineral family.
Its characteristic green coloration is particularly influenced by trace elements such as chromium and vanadium.
Color, clarity, and “Jardin”
Natural emeralds often possess inclusions and fine surface-reaching fissures. This characteristic internal appearance is frequently described in the gemstone trade with the French term “jardin” – garden.
Treatments
Improving visible clarity through oil, resin, or other filling materials in surface-reaching fissures is a well-known and widely used treatment for emeralds.
Care of emerald
Despite its Mohs hardness, natural fissures and inclusions can make an emerald more sensitive to impacts. Clean it preferably with lukewarm water, mild soap, and a soft cloth or a soft brush.
Ultrasonic and steam cleaners should be avoided, especially with clarity-enhanced emeralds.
Tradition and meaning
Emerald is the traditional birthstone of the month of May and has been counted among the most important green gemstones for millennia.
Topaz
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Mineral: Topaz
Color: Colorless, blue, yellow, orange, pink, brown, and other shades
Mohs hardness: 8
Birthstone: November
What is topaz?
Topaz is a distinct mineral species with a wide variety of colors. It can naturally occur as colorless or in shades of yellow, brown, orange, pink, and more rarely, blue.
Blue Topaz
Intensely blue topaz is particularly well-known in modern jewelry. However, naturally vibrant blue topazes are rare.
A large portion of the blue topaz on the market achieves its color through irradiation and subsequent heat treatment of originally colorless or very light-colored topaz.
Hardness does not mean durability
Although topaz has a Mohs hardness of 8, it also possesses a distinct cleavage. A hard impact from an unfavorable angle can therefore lead to chipping or breakage.
Care of topaz
Topaz should be cleaned with lukewarm water and mild soap. Ultrasonic and steam cleaning as well as extreme temperature changes should be avoided.
Tradition and significance
Along with citrine, topaz is one of the traditional birthstones for the month of November.
General care of gemstone jewelry
Proper care depends on the type of gemstone, inclusions, potential treatments, and the construction of the piece of jewelry.
- Remove jewelry before exercising, doing housework, or engaging in activities involving heavy mechanical stress.
- Avoid strong impacts and pressure on gemstones and settings.
- Minimize contact with perfume, hairspray, cosmetics, and harsh cleaning agents.
- Store pieces of jewelry separately if possible.
- Avoid ultrasonic and steam cleaning if the treatment is unknown.
- Have settings and the security of the stones checked regularly.
Why are gemstones treated?
Various gemological treatments are used on colored gemstones, such as heat treatment, clarity enhancement, or irradiation. Such procedures can, among other things,
