For a metal to be deemed precocious - the reasons have as much as to do the economics, as they have to with chemistry. So the fist thing I would like to say is that like everything in this world only those things have value which we decide to give value to. Obviously our decision of considering gold worthy of being trusted as 'precious' has several reason. Gold has been deemed precious for the following reasons:

1. Rarity: 

Gold is a rare metal. Humans desire that which is rare. In fact this law gives us the very bases of pricing of goods in market. But other elements in periodic table are rare too. 

Some are gases/volatile/flammaable - thus difficult to capture and store. 

Some are liquid and thus difficult to handle. 

Some are poisonous or  radioactive and thus harmful.

Some are so rare that we just don't have enough of it to make it work as money. Gold not too abundant or too rare.

Some are so reactive that they just wont stay pure.

GOLD - has none of that. Gold is rare in way that is useful to us. 

2. Purity:

Gold usually can occur in its pure form. It doesn't easily gets mixed with other elements and can stay relatively safe from the environment without corroding away.

3. Usefulness as Store of Value/Money:

The above properties of its special kind of rarity and purity makes it valuable. It rarity makes sure that there is only a limited supply available and thus prevent over inflation. Its purity(being a noble metal) makes sure that it is not easily corrupted (similar to counterfeit of fiat money).

4. Malleability:

Gold is easy to work with. You can make out if what you want - much easily than other metal. Thus it is easy to make coins and bars out of it. We can also easily makes jewellery out if it and thus we have its ornamental use

5. History

Gold has been established as a trusted form of money since ancient times. This means a lot more than we can imagine.