The main May sign of the Zodiac is Taurus and the second sign is Gemini. Taurus is the bull astrology sign for those born from April 21 to May 21 and Gemini is the twin astrology sign for those born from May 22 to June 21. The start and end days of each sign can vary by a day or two each year, depending on the solar system position in that particular year.
The list of Zodiac gemstones per sign varies from source to source, so the main reference we use is the historical Curious Lore of Stones by George Frederick Kunz. These groups of stones are also known as Zodiac birthstones. Other Zodiac crystal sets may not be based on historical birthstones but are chosen by crystal healing experts to complement the typical personality of each Zodiac sign. In some cases one or two of the crystals may also match with that sign's birthstones.
The primary gemstones for the May signs are Sapphire for Taurus and Agate for Gemini.


May Sign of Zodiac – Taurus (Apr 21 to May 21)
The main gemstone for Taurus is Sapphire and other stones include Azurite, Coral, Amber, Emerald, Rose Quartz and Turquoise. Taureans are fortunate to have two of the four precious gemstones - Sapphires and Emeralds.
Sapphire is a beautiful gemstone that is highly valued for its stunning deep royal blue color.
The formation of sapphires takes place over many eons in the Earth’s crust and requires specific conditions to form. It is composed of trace elements such as iron, titanium, chromium and vanadium, which give the stone its unique blue hue. The more iron in a deposit, the darker the blue color. Sapphires also form in other colors such as yellow, pink or green.
The formation process of sapphire involves high temperatures and pressures that force the trace elements to combine with aluminum oxide molecules to create a particular crystal structure. This crystal structure gives sapphire its unique appearance and makes it one of the most sought after gemstones in the world.


Taurus Zodiac Stone Emerald
Emeralds are one of the most precious and beautiful gems in the world. They have been used for centuries in jewelry, ornaments, and other decorative objects. Emerald is the traditional birthstone for those born in May.
Emeralds form in a variety of ways, from magma chambers to hydrothermal vents. The color of an emerald is determined by its trace elements, such as chromium and vanadium. These elements give the gemstone its unique green hue. There are also different types of emeralds, including Brazilian emeralds and Colombian emeralds.
In addition to being used as jewelry and decorations, emeralds can also be used for industrial purposes such as cutting tools or abrasives. They may even be used in medical treatments such as radiation therapy or cancer treatment drugs.
No matter how they are formed or what they are used for, it is clear that emeralds will continue to fascinate us with their beauty and mystery for years to come.
May Sign of Zodiac – Gemini (May 22 - Jun 21)
The main gemstone for Gemini is traditionally Agate and other crystals include Chrysoprase, Citrine, Pearl, White Sapphire and Moonstone
Agate is a type of cryptocrystalline quartz that is formed in cavities and veins of igneous rocks. It is composed of silicon dioxide, which gives it its unique colors and patterns. Agate can be found in many different colors, including red, blue, yellow, green, purple and brown. The most common pattern found on agates are bands or stripes that form concentric rings or swirls.
The formation of agates involves a combination of trace elements such as iron and aluminum that give the stone its unique coloration. In addition to these trace elements, agates can also contain other minerals such as mica or calcite which can create interesting patterns on the surface.
Agates have been used since ancient times for jewelry making and decorative purposes due to their beautiful colors and intricate patterns. They are still popular today for their various uses in jewelry making and home décor items such as bookends and paperweights.


Gemini Zodiac Stone Chrysoprase
One of the Zodiac crystals for Gemini sign is Chrysoprase. This affordable green gemstone is also an alternative May birthstone to the traditional emerald.
Chrysoprase is a type of chalcedony containing small quantities of nickel which causes the green hues. Shades range from deep green to beautiful apple-green.
Chrysoprase was mined primarily in Czech Republic and Poland. However a high quality deposit was discovered in Queensland, Australia which has now become the major source. Chrysoprase from Australia is known as Australian Jade. Other deposits occur in the USA, Russia and Germany.
The color, even texture and translucence makes this gemstone ideal for cameos and beads.
Taurus Bracelet and Crystal Set
Conscious Items recommend Tigers Eye, Rose Quartz, Chalcedony, Serpentine Jade and Black Tourmaline as five stones for Taurus. "They empower bulls to regain emotional control and rein in their stubborn side."
Gemini Bracelet and Crystal Set
Conscious Items recommend Obsidian, Tigers Eye, Chalcedony, Leopard Jasper and Clear Quartz as five stones for Gemini. "They help Gemini gain better self-control while simultaneously feeding their playful attitude."
References:
Zodiac Gemstones: Curious Lore of Stones by George Kunz.
Geology: Geology.com and Gemological Institute of America