Diamond is the modern, traditional and ayurvedic  gemstone for April, opal is the mystical gemstone with quartz and white sapphire being   alternate  gemstones.
      Legend has it that Europeans first discovered African diamonds in a Shaman's leather pouch. The African Shaman used his diamonds as Shamans of the world use quartz crystals. Anciently, diamonds were worn as unpolished stones. They were treasured for their beauty and powers. The Philosopher's Stone: The diamond is an ancient symbol of the perfected man whose divine spirit shines forth. As the rough diamond is dull and lifeless
when first removed from the earth, so the spiritual nature in its "earthly" state  reveals little of its inherent luminosity. In the hands of the skillful lapidary, the diamond is transformed into a sparkling gem from whose facets pour streams of rainbow colored fire, so upon the lathe of the Divine Lapidary, the spirit of man is ground and polished until it reflects the glory of its Creator from every atom. He lives by spirit.  Kings, in old days, led the battles on the battle fields. They wore heavy leather breast plates studded with diamonds and other precious stones.  Because it was believed that diamonds were fragments of stars and the tear drops of the Gods, the diamonds possessed magical qualities of the Gods and had powers far beyond the understanding of common man. The warriors stayed clear of the Kings and those who were fortunate enough to have the magical diamonds in their breast plates. So, they survived the wars by the magic of the diamonds and were blessed by the Gods and had lives of good fortune. Much of this lore still lives today in a simply saying, "diamonds are a girls best friend." In ancient Greece and Summaria, diamonds were the status symbols of Kings and the very wealthy. The Greek word adamas," meaning unconquerable and indestructible, is the  root word of the word diamond. Diamonds were worn because they were thought to give a person strength, invincibility, courage, and magical powers over the dark side of life. Rainbows of color gave the stones magical powers over the evil eye of the sorceress and magicians of the day.
    Of the myriad legends surround the glittering diamond, one of the most widespread was the belief that it could
determine guilt or innocence. The test was simple. If the accused was guilty, the adjudicating diamond would grow dark. In the presence of innocence, however, it would glow with increased brilliance. Symbolic of innocence,   justice, faith, and strength, the diamond was believed to make its wearers courageous and to make them victorious   over their enemies. When set in gold and worn on the left side, it had the power to drive away nightmares and to tame wild beasts.
        Because a diamond was believed to sweat in the presence of poison, it was used to detect it. The gem frequently was worn to ward off poison, yet it was believed to be deadly when swallowed.
        The finest diamonds were believed capable of reproducing themselves. It was thought that these special stones, when moistened with morning dew and left in the dark, would multiply. Other uses for diamonds were to ensure strong bones, to stop lechery, and to protect both the mother and baby during childbirth. The Hindus believed that this brilliant gem owed its origin to bolts of lightning striking rocks. The talismanic virtue of the diamond was said to be lost if the stone was purchased. To be effective the gem had to be given as a pledge of love or friendship. April's birthstone is said to be the most potent when set in steel.