Aquamarine and blue topaz are both beautiful blue gemstones that can be used for jewellery, but they have some differences that can help you tell them apart.
Look at the colour: Aquamarine is usually a lighter, more pastel blue-green colour, while blue topaz can range from a pale blue to a deeper, more saturated blue colour. Aquamarine also tends to have a higher transparency than blue topaz, which can have a strong refraction and sparkle.