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Precious and Semi-Precious Gemstones

Learn all about both precious and semi-precious gemstones with our guide to the top 12 most popular gemstones common to jewelry shoppers.

Precious and Semi-Precious Gemstones

A gemstone is a cut and polished piece of mineral crystal often used for jewelry. Although most gemstones are generally hard on the Mohs scale of mineral hardness (a qualitative scale from 1 to 10 characterizing scratch resistance of minerals), some soft minerals are utilized in jewelry because of their brilliance or other aesthetic features. Other attributes that add value to gems include rarity and reputation. Gemstones have captivated people since the dawn of time, and they have long been utilized in jewelry. 


Amethyst was formerly considered one of the precious gemstones (along with diamond, sapphire, ruby, and emerald) until enormous reserves were discovered in places like Brazil in the 18th century. Since then, its value has plummeted. As a result, it has now been classified as a semi-precious gemstone. This does not detract, however, from its beauty and allure as a gemstone with vibrant purple hues, ranging from light pastel to regal and majestic colors.

Amethyst is quartz by nature which is purple. Amethyst has a specific gravity of 2.63 – 2.65. and refractive index of 1.544 – 1.553. It was highly uncommon and expensive until the turn of the twentieth century.


Alexandrite is a highly unique and unusual color-change variant of the mineral chrysoberyl that is often characterized as “emerald by day, ruby by night” by gem lovers. Alexandrite is considered to be a rare and precious gemstone. It was first discovered in the Ural Mountains of Russia in the 1830s and is presently found in Sri Lanka, East Africa, and Brazil. However, quality stones are  extraordinarily uncommon and precious, making alexandrite one of the more rare and expensive gemstones in the jewelry market. Much of the alexandrite jewelry sold by jewelers are synthetic. Be sure to confirm whether the jeweler lists them as real and genuine gemstones.

Two factors primarily contribute to the rarity and cost of alexandrites. First, the closer the hues are to pure green and red, the more valuable the gem is. The second thing that increases alexandrite’s value is its ability to change color. Its chemical formula is BeAl2O4 with a refractive index of 1.746 to 1.755 and birefringence of 0.008 to 0.010. Alexandrite gemstone has a specific gravity of 3.73 and Mohs hardness of 8.5.


Aquamarine is a lovely gemstone that belongs to the big beryl species, including emerald and morganite. It is also regarded as a semi-precious gemstone. Aquamarine is the term given to gem-quality beryl specimens ranging from greenish-blue to grey-blue. Regardless of the stone’s tone or saturation, aquamarine jewelry can be a very sought after gemstone, and is more costly than your average semi-precious stone. Aquamarines can vary from a faint, almost unnoticeable shade to a deep, bright hue.

Aquamarine is one of the more demanding gemstones, with a Mohs hardness of 7.5 to 8. The chemical composition of aquamarine is Be3Al2Si6O18, and it has a specific gravity of 2.6 to 2.8.


Citrine is considered a semi-precious gemstone and is a yellow quartz type stone with a beautiful sheen and exceptional clarity. As a Quartz variety, the chemical composition of citrine is SiO2, having a specific gravity of 2.651 and a refractive index of 1.544-1.553. The yellow in citrine rings and jewelry can be bright, beautiful and radiant.


Emeralds are the most precious (apart from diamonds) and the rarest gemstone. They are labelled as the crown jewels of monarchy and romance. Emeralds are distinguished by their vivid green hue and natural inclusions, which give each one a unique appearance. However, being such a rare and sought after stone, emeralds tend to be lower quality with many inclusions and sometimes even fissures in the stone, unless you pay a premium to get a higher quality emerald, that is one reason emerald engagement rings can be as expensive as diamond rings. When shopping for an emerald, ask for an “A” rated or higher quality stone, which will come with a premium in price compared to other more common, semi-precious gemstones.

The chemical composition of emerald is Be3Al2(SiO3)6, with a Mohs hardness of 7.5 to 8 and specific gravity of 2.7 to 2.8.


Garnet is considered a semi-precious gemstone. Garnets are commonly associated with the color red. However, they can also be orange, pink, green, black, or honey brown. There are also varieties like rhodolite garnet. Garnet refers to various minerals, each of which is called by its color. There are multiple garnets available, including Mozambique (which is the most common variety that you will find in most garnet rings and jewelry), but also Almandine, Andradite, Grossular, Pyrope, Rhodolite, and Spessartine. Garnets have a refractive index of 1.714-1.888 and a specific gravity of 3.47-4.15


Opal is a kind of hydrated silica and considered a semi-precious gemstone. The common opal’s hue is usually colorless, although fine-grained impurities can add streaks of grey, brown, yellow, or red. Opals make fine jewelry and have a refractive index of 1.37 – 1.47 and a specific gravity of 2.15+0.08 −0.90.


The vibrant olive-green Peridot is considered a semi-precious gemstone, although it tends to be a little rarer and slightly more expensive than your average semi-precious stone. Individual peridots might be yellowish-green, greenish-yellow, brownish-green and olive-green in color. The amount of iron in the crystal structure determines the strength and hue of the distinctive green color. Peridot gemstones have a refractive index of 1.64–1.70 and a specific gravity of 3.2–4.3.


The ruby is a foundational precious gemstone and included among the big 3 (ruby, sapphire and emerald) with a slighltly purplish red to a bright, brilliant red hue that characterizes the best ruby jewelry. Rubies have the highest price per carat of any colored stone and are comparable to the emerald and sapphire in price and value. Color differences are caused by trace elements that become part of the crystal structure. The trace element chromium is responsible for ruby’s red hue. As a result, the ruby is one of the most precious jewels in the colored stone industry. The ruby has a Mohs hardness of 9.0 and a specific gravity of 3.97–4.05.


The Sapphire is a valuable precious gemstone made of aluminum oxide (-Al2O3) with trace quantities of other various elements, including iron, titanium, chromium, vanadium, and magnesium. Sapphires come in various colors, including blue, pink, purple, violet, peach, orange, green, brown, and grey. There are also white sapphires, which are colorless sapphires. The refractive index of sapphire is 1.762 to 1.770, birefringence is 0.008 to 0.010, specific gravity is 4.0, and Mohs hardness is 9. Sapphires are one of the most sought after precious gemstones in existence and are a very popular choice for jewelry, including sapphire as sapphire and diamond rings and engagement rings.


Tanzanite has been dubbed “the gorgeous blue gem” and “the most important gem discovery in 2000 years,” among other accolades. It’s no wonder, therefore, that this gleaming bluish-violet diamond is in high demand. However, tanzanite is still classified as a semi-precious stone under conventional categorization, even though you may pay near-precious gemstone prices for the violet stone. The specific gravity of tanzanite is 3.10–3.38 with a refractive index of 1.69–1.70 making it a perfect candidate for use as a trendy or fashionable jewelry.


Topaz is one of the most popular semi-precious gems for jewelry. Topaz is found in crystals that are much bigger than those of many other valuable stones. It is an affordable, valuable blue stone that works well in more significant jewelry pieces because of its beautiful color and quality. Being a semi-precious gem, a ver high quality “A”, “AA” or “AAA” Topaz can be obtained for relatively cheap. Topaz is available most commonly in blue varieties, including Swiss Blue, Sky Blue and London Blue Topaz. Other colors include pink topaz, yellow and fiery orange. Topaz is a bright and sparkling stone that comes in warm and cold tones. Topaz has a refractive index of 1.619 to 1.627 with a specific gravity of 3.53 and Mohs Hardness of 8, making it perfect for jewelry use.

Purchasing Gemstone Jewelry

Was this precious and semi-precious gemstone guide from Apples of Gold Jewelry a benefit and a help to you? Consider perusing our unique collection of gemstone rings and jewelry, available in 14k yellow and white gold, with or without diamonds and as stylized jewelry for fashion or high-end rings for as highly sought after real gemstone engagement rings with precious metals.

Would you like one of our jewelry pieces in a different gold color or metal like platinum or do you see a ring setting you like but want a different gemstone? Apples of Gold Jewelry has virtually every option available, even if not listed on our website. Simply contact us for more information!

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