The Complete Gemstone Guide

From precious stones like rubies and sapphires to a rainbow of semi-precious options, our comprehensive guide will help you understand and appreciate the beauty, value, and unique characteristics of gemstones.

Precious Gemstones

Historically, only rubies, sapphires, emeralds, and diamonds were considered "precious" gemstones due to their rarity, hardness, and cultural significance. Though the precious/semi-precious distinction is less relevant in modern gemology, these stones continue to be highly valued for their beauty and durability.

Ruby

Known for its deep red color, ruby is a variety of the mineral corundum and one of the most valuable gemstones.

Color:

Red (from light pink to deep crimson)

Hardness:

9 on Mohs scale

Birth Month:

July

Value Factors:

Color (deep "pigeon blood" red is most prized), clarity, size, and origin

Care Level:

Low maintenance; suitable for daily wear

Sapphire

Another variety of corundum, sapphires come in all colors except red (which would be ruby). Blue sapphires are the most popular and valuable.

Color:

Most commonly blue, but available in nearly all colors including pink, yellow, green, purple, and colorless

Hardness:

9 on Mohs scale

Birth Month:

September

Value Factors:

Color (royal blue most valued), clarity, size, and origin

Care Level:

Low maintenance; suitable for daily wear

Emerald

A variety of beryl, emeralds are prized for their lush green color and historical significance.

Color:

Green (from light to deep rich green)

Hardness:

7.5-8 on Mohs scale

Birth Month:

May

Value Factors:

Color (vivid, slightly bluish-green is most valuable), clarity, size, and minimal treatments

Care Level:

Requires careful handling; avoid impacts and harsh chemicals

Semi-Precious Gemstones

"Semi-precious" encompasses all other gemstones beyond the traditional "precious" ones. Many of these stones can be more rare, valuable, and beautiful than some "precious" gems, demonstrating the outdated nature of this classification. These gems offer a wider range of colors, properties, and price points.

Amethyst

Purple variety of quartz, once considered as valuable as rubies until large deposits were discovered.

Color:

Purple (from pale lilac to deep purple)

Hardness:

7 on Mohs scale

Birth Month:

February

Care:

Moderate; avoid prolonged sunlight exposure

Aquamarine

A blue to blue-green variety of beryl, named after the Latin words for "sea water".

Color:

Light blue to blue-green

Hardness:

7.5-8 on Mohs scale

Birth Month:

March

Care:

Moderate; avoid high heat and harsh chemicals

Topaz

Classic gemstone available in various colors, with blue topaz being the most popular commercially.

Color:

Colorless, blue, brown, yellow, pink, purple, red (rare)

Hardness:

8 on Mohs scale

Birth Month:

November

Care:

Moderate; can crack if exposed to rapid temperature changes

Opal

Known for its unique play of colors, opal contains microscopic spheres that diffract light to create flashes of color.

Color:

White, black, or fire opal with spectacular play of colors

Hardness:

5.5-6.5 on Mohs scale

Birth Month:

October

Care:

High; avoid water, heat, and impacts

Peridot

One of the few gemstones that occurs in only one color, varying from yellowish-green to olive.

Color:

Yellow-green to olive-green

Hardness:

6.5-7 on Mohs scale

Birth Month:

August

Care:

Moderate; avoid high heat and sudden temperature changes

Garnet

A group of minerals with similar properties but varying in chemical composition and color.

Color:

Most commonly red, but also green, orange, yellow, purple, and color-changing

Hardness:

6.5-7.5 on Mohs scale

Birth Month:

January

Care:

Low to moderate; generally durable

Understanding Gemstone Treatments

Most gemstones on the market today undergo some form of treatment to enhance their appearance. These treatments are accepted practices in the industry when properly disclosed to the buyer. Understanding common treatments helps you make informed decisions and properly care for your gems.

Treatment	Description	Common For	Disclosure Impact
Heat Treatment	Heating gemstones to enhance or change color, improve clarity, or alter other characteristics.	Sapphires, rubies, aquamarine, amethyst, topaz, tanzanite	Standard and widely accepted with proper disclosure
Oiling/Filling	Filling surface fractures with oils, resins, or glass to improve clarity and appearance.	Emeralds (oil), rubies (lead glass), diamonds (fracture filling)	Must be disclosed; significantly affects value compared to untreated stones
Irradiation	Exposing gemstones to radiation to alter their color.	Blue topaz, certain diamonds, tourmaline, pearl	Must be disclosed; regulated by various authorities
Dyeing	Adding coloring agents to porous gemstones to change or enhance color.	Pearls, corals, turquoise, jade, onyx	Must be disclosed; reduces value compared to natural counterparts
Surface Coating	Applying thin layers of chemicals to alter or enhance a gemstone's color or appearance.	Topaz, quartz, tanzanite simulants	Must be disclosed; significantly reduces value

Frequently Asked Questions

What's the difference between precious and semi-precious gemstones?

Historically, only diamonds, rubies, sapphires, and emeralds were classified as "precious" gemstones, with all others considered "semi-precious." This distinction originated in ancient times based on rarity and value, but is considered outdated by modern gemologists. Today, many "semi-precious" stones like fine alexandrite, spinel, or Paraíba tourmaline can be more valuable than some "precious" stones.

Are synthetic gemstones "fake"?

Synthetic gemstones are not "fake"—they have the same chemical composition, crystal structure, and optical properties as their natural counterparts. They're real gemstones created in laboratories rather than mined from the earth. Synthetics differ from simulants (like cubic zirconia or glass), which only mimic the appearance of another gemstone but have different chemical and physical properties.

How should I care for my gemstone jewelry?

Care requirements vary by gemstone. As a general rule, clean most hard gemstones (sapphires, rubies, garnets) with mild soap, warm water, and a soft brush. Softer or more porous stones (emeralds, opals, pearls, turquoise) should never be soaked and should be wiped with a damp, soft cloth. Store gemstone jewelry separately to prevent scratching.

What gemstones work well for engagement rings?

Beyond diamonds, sapphires are an excellent choice due to their durability (9 on Mohs scale) and variety of colors. Rubies offer similar hardness with romantic red hues. Moissanite has become popular for its diamond-like brilliance and exceptional hardness (9.25). For colored options with good durability, consider spinel, alexandrite, or garnet varieties like tsavorite. Avoid soft stones like opals, pearls, or turquoise for daily-wear rings.

How can I tell if a gemstone is natural or treated?

Without specialized equipment, identifying treatments can be challenging even for professionals. The best approach is to purchase from reputable dealers who provide full disclosure and certification from recognized laboratories (GIA, AGL, etc.) for valuable stones. When in doubt, have important pieces evaluated by an independent appraiser or gemological laboratory.

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