Gold is another store of value, but not that unstable. It reached 2000$ recently and was above 1000$ for many years. Those who invested in gold back in 1900 would have made a great choice since it costed only 20$ back then if I'm not wrong. (Although dollar was way more strong than now)
Bitcoin can lose 500$ within one night. Gold can't. Why that?
Gold has been in use for ages, while Bitcoin came up in the 20th century. And gold is a Fiat currency, its globally accepted as a means of exchange, while most countries don't know what Bitcoin is.
Correction - Bitcoin came up in the 21st century!

Bitcoin is volatile because it has no regulation, and all existing exchanges at the moment resemble Wild West! Huge holders can manipulate the price as they want!