Rubies and red spinels are very similar in terms of physical and chemical properties
Rubies and red spinels are commonly found in mines. Due to their great similarity, the two Minerals were not separated from each other until recent years, so most red pearls were considered rubies in ancient times.
In 1783, a French mineralogist named Louis Rom de lisle introduced Pearl as a separate mineral from ruby. From a Chemical point of view, Ruby is a combination of Aluminum oxide corundum (AL203) and magnesium aluminum oxide (MgAL204), while rubies are in a "hexagonal crystal" hexagonal crystal system. They form "Trigonal", forming Spinel Gemstones in the isometric crystal system, "Cubic cube" and "Octahedral".
The density and light emission index of rubies are slightly higher than those of rubies, but this difference is so significant that it distinguishes the two seemingly similar stones. In fact, differences in hardness and weight helped ancient Gemstone carvers in Sri Lanka, South of Asia and Burma understand the difference between rubies and spinels before gemology was introduced to the world as a science.