Selling gold that contains zircon stones for the price of pure gold
Question

                We sell gold which contains zircon stones for the price of gold. Please note that this is obvious to the purchaser and he knows about this. What is the ruling on this sale?.
Praise be to Allah.
    Selling gold that contains zircon stones for the price of 
    gold is something that is subject to further discussion. 

    If it is being sold for silver or paper money, there is 
    nothing wrong with that, so long as it is visible to the eye and the 
    purchaser knows about that, as you have mentioned. If it is being sold for 
    gold, then the stones must be separated from the gold so that the amount of 
    gold may be known, and it may be ensured that equivalent amounts of gold are 
    exchanged. This is indicated by the hadeeth of Faddaalah ibn ‘Ubayd about 
    the sale of a necklace, which was narrated by Muslim (1591) who said: When 
    the Messenger of Allaah  (peace and blessings of Allaah be upon him) was 
    in Khaybar, a necklace containing pearls and gold, which was part of the 
    booty, was brought to him to be sold. The Messenger of Allaah  (peace 
    and blessings of Allaah be upon him) ordered that the gold in the necklace 
    be separated from it, then the Messenger of Allaah  (peace and blessings 
    of Allaah be upon him) said to them: “Gold for gold, weight for weight.” 
    According to another report: “It should not be sold until it has been 
    separated.” 

    Al-Nawawi said in Sharh Muslim: 
This hadeeth shows that 
    it is not permissible to sell gold with something else for gold until it has 
    been separated, and gold should be sold for gold by weight, but it may be 
    sold for anything else however one wishes. Similarly silver combined with 
    anything else cannot be sold for silver… whether the amount is a little or a 
    lot. This was narrated from ‘Umar ibn al-Khattaab (may Allaah be pleased 
    with him) and his son, and a number of the salaf, and it is the view of 
    al-Shaafa’i and Ahmad. End quote. 

    Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was 
    asked about selling gold which is combined with zircon stones for gold of 
    the same weight. He replied: 

    This transaction is haraam, because it involves riba, as it 
    is adding something to the gold by giving gold in return for the gems etc. 
    This is like the necklace which was mentioned in the hadeeth of Faddaalah 
    ibn ‘Ubayd, who bought a necklace that contained gold and pearls for twelve 
    dinars, and he separated it and found that it contained more, and the 
    Prophet  (peace and blessings of Allaah be upon him) said: “It should 
    not be sold until it has been separated.” End quote. 

    Shaykh Muhammad ibn ‘Uthaymeen.  
Majmoo’at As’ilah fi Bay’ wa Shira’ al-Dhahab.