Howlite is a Borate mineral with grey and white colours and dark grey veins, while Turquoise is a rare blue-green mineral of hydrated Copper and Aluminium Phosphate. Although Howlite is a beautiful stone and holds its own value, sometimes it is marketed as Turquoise after being dyed blue and also referred to as white Turquoise but there is no relationship between the two other than having some resemblance with the veining.
There are several ways to tell if it is real Turquoise -
1. Pricing -
Genuine Turquoise is much more expensive than fake Turquoise or dyed Howlite. In the Australian market, it will not be sold for less than $10 a small raw piece.
2. Colour -
Essentially, Copper contributes to the blue colour and when mixed with Phosphorus and water, this will form the green-blue colours found in the Turquoise stone. However, depending on the degree of each element and this will change the resultant colour of each piece.
Hence dyed Howlite stones will generally have the same colour throughout.
3. Mohs Hardness Scale or Scratch Test
The Mohs scale ranges from 1 to 10 to determine scratch resistance of a mineral with a harder material being able to scratch a softer material.
4. Acetone Test
Dab a cotton ball or swab into some acetone or nail polish remover. Rub it on a section of the stone and if some dye is removed, then it is not real. There should not be any green-blue residue particularly if it is polished when you try this method on genuine Turquoise.
Note:
Feel free to have a read as it is only a positive to learn as much as possible and know what you are buying.