Elagabalus, also known under the Greek name Heliogabalus, was the 25th emperor of the Roman Empire. His reign was short, lasting from only 218 until 222 CE.
Much controversy has always surrounded his life, from ancient times until now. He was murdered in a riot by his own guard, after he stripped his younger cousin Severus Alexander (appointed co-emperor by his grandmother, probably to later replace him) of all his titles and revoked his consulship.
He was openly gay, having a relationship with a slave named Hierocles, whom Elagabalus referred to as his husband. He also allegedly later married another man named Zoticus, an athlete, though this is disputed, the only source being the ancient text Historia Augusta.
History lessons aside, let's get to the numismatic aspects of your coin.
The silver coins issued by Elagabalus were antoniniani and denarii (singular antoninianus and denarius). These coins can be told apart from their weight - an antoninianus should weigh around 3 grams, commonly just over, such as 3.1 to 3.2 grams. A denarius should weigh more, up to 4 grams. However, some smaller denarii minted towards the end of his reign can also weigh as little as 3 grams.
The surefire method for telling denarii and antoniniani from one another is simple: on an antoninianus, the emperor wears a radiate crown with upward spikes, while on a denarius, he wears a laureate (wreath) crown.
Now, as far as what the coins are worth, here are some very approximate catalog values:
worn: $30 US dollars approximate catalog value
average circulated: $40
well preserved: $75
fully uncirculated: $350
average circulated: $35
well preserved: $65
fully uncirculated: $275
Remember that these ancient coins each stand on their own merits. Coins with great eye appeal will be worth a lot more, and coins with terrible eye appeal will be worth a lot less than the values quoted above, even if the wear on the coin fits with the table. Also, these are catalog values. Refer to the 'Important Terminology' link in the menu on the top left in order to properly interpret these values.
Some legends found on the antoniniani include 'P M TR P COS P P' with a woman seated left holding a scepter, 'FIDES EXERCITVS' with a crowned man seated left holding a standard and an eagle, and 'FIDES MILITVM', with a man standing, holding a standard and a vexillum, also a type of battle standard.
Some legends found on the denarii include 'FORTVNAE REDVCI', with a man standing left holding a globe and a cornucopia, a horn of plenty; 'INVICTVS SACERDOS AVG' with a man standing left with his hand over a sacrificial altar, holding a club; and 'IOVI CONSERVATORI' with Jupiter standing left, holding a thunderbolt and a spear, often with a standard at his side.