Top diamond and gemstone grading


The purple Alexandrite stone is a rare variety of the chrysoberyl mineral, which absorbs light in a unique way. This is why the Alexandrite changes its color – green in daylight, and purplish-brown in soft light. This color change is known is colloquial language as “emerald by day, ruby by night”, or “the alexandrite effect.”


Amber is fossilized tree resin. High pressure and high temperatures transform the resin first into copal, and then into amber. For this to happen, the resin must be resistant to decay. Most resins decay, making those that survive more valuable.


Amethyst is a type of quartz whose color ranges from light lavender to deep violet. Until the 18th century, amethyst was one of the most valuable gemstones along with diamonds and sapphires. However, since the discovery of extensive deposits in Brazil and other countries of the new world, it has lost most of its value and is now considered a semiprecious stone.


Ametrine is a variety of quartz and a mixture of amethyst and citrine, which produce its yellow and purple colors. Its color transition is influenced by fluctuations in temperature and pressure during its formation. According to legend, Ametrine was first introduced to Europe by a conquistador, who gave it as a gift to the Spanish Queen in the 17’th century.


Aquamarine is a bluish-green variety of beryl created by heat. The value of aquamarine is determined by weight, color, cut and clarity. Historically, the stone served as a symbol for youth and happiness. Ancient  Romans believed it can protect sea travellers due to its aqua color.


Citrine is a popular type of quartz, known as a symbol of abundance. Most citrine stones are amethysts that have undergone heat treatment. It comes in sunny shades of yellow and orange. There are three types of Citrine – natural citrine (typically more expensive), heat-treated Citrine (initially Amethysts), and smoky Citrine (Citrine combined with some smoke quartz).


Diamond is a solid form of carbon whose atoms are arranged in a crystal structure called diamond- cubic. Diamonds are the hardest mineral, with the highest thermal conductivity, hence it popularity in various industries that use cutting and polishing tools. Most natural diamonds are 1 to 3.5 billion years old and were carried to the surface through volcanic eruptions.


Emerald is a variety of the mineral beryl. Its green color is derived from its chromium component. Most emeralds are relatively soft, with inclusions and cracks. For this reason, most of them are oiled before reaching the market, to fill in the cracks.


Garnets are a set of similar minerals that form a group in various colors. All garnets have the same crystal structure, but they vary in their chemical composition. Garnets are divided into more than twenty species, five of which have value as gems.


Iolite, known also as Cordierite, is a magnesium- iron - aluminium cyclosilicate. It is found in  pelitic rocks. Its color ranges from sapphire blue to yellowish gray or light blue. Due to its shade, it is sometimes used as an inexpensive substitute for sapphire.


Jade is a mineral that is typically green, sometimes yellow or white. Jade is actually two kinds of minerals, nephrite and jadeite, but this was not known until the 19th century. Until then, it was assumed that they are the same mineral. Nephrite comes in a creamy white form or light green, while jadeite comes in various colors.


Kunzite is named after the famouse gemologist George Frederick Kunz, who discovered this unique variety of spodumene mineral. Its light pink-violet color is derived from its manganese component. Its color is most visible when the viewer looks down the length of the crystal. For this reason, some cutters make a deep cut to emphasize its pinkish color.

Lapis lazuli

Lapis Lazuli is a deep-blue gem made mainly of lazurite mineral and mined in Afghanistan. It exists in lower quantities in some places in Asia and the Americas. Lapis lazuli usually occurs in crystalline marble as a result of intrusion of magma into the cooler layer of the earth.


Moonstone is known for its moon-like, bluish white color and its fragile consistency. The more transparent the stone and the bluer its adularescence, the higher its value. Its hue is created by alternating layers of orthoclase and albite. Adularescence is caused by the diffraction of light against the alternating layers. The blue sheen is produced if the albite layers are thing enough.


Morganite is a gem whose color ranges from pale pink to bluish pink, derived from traces of manganese. The color is mostly pale. One of the interesting features of morganite is its intense red fluorescence when exposed to X-rays. Morganites with stronger colors are more expensive. Most morganite are mined in Brazil.


Opal is a hydrated amorphous form of silica, with high water content (up to 20%). Because of its amorphous character, it is classified as a mineraloid, not a mineral. It can be found in areas of low temperatures, in any kind of rock, usually limonite,  sandstone, rhyolite, marl, and basalt.


Pearls are produced from the soft tissue of a shelled mollusk or another animal. It is composed of calcium carbonate  deposited in concentric layers. The typical pearl is round and smooth. The most expensive pearls are found in nature and are extremely rare. Most commercial pearls are cultured or farmed  from pearl oysters and freshwater mussels.


Peridot  is a magnesium-rich variety of the olivine mineral. Its green color is produced by the iron content in the gem – the higher the iron quantities, the greener the gem. Peridot can be found in basalt stones and pallasitic meteorites, since it is formed in high temperatures starting from 600°C. It is one of the few gems formed above ground.

Rose quartz

Rose quartz has been known since 7,000 B.C. Most rose quartzes are solid light pink, but can sometimes come in deeper varieties called strawberry rose or in pale purple called lavender rose quartz. It is composed of silicon dioxide molecules formed by heat.


Ruby is one of the most known and highly prized gems. Blood-red rubies are the highest in value. All natural rubies have imperfections such as color impurities and inclusions of rutile needles known as "silk". These needles help us distinguish between natural and synthetic rubies.


With their rich, deep-blue color, sapphires are one of the most precious, expensive gemstones. They are a variety of the mineral corundum. Some sapphires come in other colors, the famous ones being red – those are rubies. Sapphires are used not only for jewelry, but also for industries that rely on infrared optical components with high durability.


Spinels are part of the spinel group of minerals. They come in a variety of shades, including colorless. Some spinels such as the Black Prince's Ruby and the "Timur ruby” gained notoriety. The transparent red spinels were also popular for a while and were called spinel-rubies or balas rubies. Before the emergence of gemology as a science field, they were often cofused with rubies.


Sunstones come in a range of colors, with an interesting optical effect - reflections derived from inclusions of red copper, hematite and goethite. This optical effect is called schiller and the color is derived from the copper content. The middle part of this crystal sparkles, with the darkest shade being in the core of the stone.


Tanzanite is a bluish-violet variety of the mineral zoisite found only in a single, small mine in Tanzania. It is known for its alternating blue, violet and burgundy colors depending on the angle and lighting conditions.


Topaz is a silicate mineral with an aluminum component. The topaz, as it is found in nature, is colorless. It is treated with heat or radiation to make it deep blue, reddish-orange, pale green, pink, or purple. Contrary to common belief, the topaz mentioned in the bible is not the modern definition of topaz, but chrysoberyl or peridot.


Tourmaline is a mineral comprised of boron with some other elements. It comes in a large variety of colors. Tourmalines were first brought to Europe by the Dutch East India Company. One of its fascinating features is its ability to attract and repel hot ashes.


Turquoise is an opaque, turquoise-colored mineral  comprized of copper  and aluminium. It is formed in various ways, including by hydrothermal fluids that leach copper from a host rock and are redeposited in a more concentrated form as a copper porphyry, with veins of copper sulfide that fill fractures in the rock.


Zircon is an accessory mineral found in felsic igneous rocks, metamorphic rocks and detrital deposits, in beach sands and stream gravels. It is highly refractive and dispersive, making it similar to diamonds in fire and brilliancy. It comes in a variety of colors.