Top 10 Most Expensive Pebbles on Earth

6. Alexandrite: Nature's Magic Color-Changing Gem

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Renowned for their amazing color-changing ability, Alexandrite is a kind of chrysoberyl among the most interesting and precious gemstones available worldwide. Under daylight or fluorescent light this amazing diamond seems green; under incandescent light it has a rich red or purplish-red colour. Often described as "emerald by day, ruby by night," this dramatic colour change is the result of the gem's unusual chemical composition and crystal structure, which absorb light differently throughout many wavelengths. Known as the "alexandrite effect," the phenomenon is so remarkable that it now serves as the benchmark for all other color-change gems tested. Originally found in Russia's Ural Mountains in the 1830s, alexandrite was named for future Tsar Alexander II and soon acquired value among the Russian nobility. The original Russian mines have long since run empty, hence fine specimens of Russian alexandrite are quite rare and valuable. Though really rare, alexandrite is now discovered in several places throughout the world including Brazil, Sri Lanka, and East Africa. Alexandrite's great value in the gemstone market is much enhanced by its rareness, especially in larger sizes and with pronounced colour change. With great stones asking even more, prices for premium alexandrite can be significant, often ranging from a few thousand to several thousand dollars per carat. Factors determining the rating include clarity, cut, size, strength and completeness of the colour change, attractiveness of the colours in both light sources. The most sought-after and precious stones are those that show a complete change from a brilliant green to a deep red with little secondary colours. Beyond its financial worth, the obsession with alexandrite reflects a special meeting of science, history, and natural beauty. Gemologists and materials scientists have been studying it because of its color-changing ability since it provides understanding of the intricate interactions between light and crystal structures. Alexandrite appeals to collectors and jewellery aficionados since it seems to have mystical qualities and changes its look with the light, therefore mesmerising spectators. One of the most sought-after and costly gemstones in the world, alexandrite is still rare, historically significant, and has unusual optical characteristics.