Unsure about your Mineral ID? If you have a white mineral it could well be quartz, but it also might be calcite. Here is how to tell if you have quartz or not.
Mineral IDs are hard to come by. When you are stuck, you need the help of professionals. Not that we here at TSC claim to be professionals, more that we know how to spot a good lump of quartz when we see one. However, that is a learned skill. We didn’t just start out as rockhounds knowing about how to test minerals for hardness or specific gravity… so here is our short guide to identifying quartz for yourself.
How to tell if your Crystal is Quartz?
Let’s say that there are three typical minerals you might find when you go hunting for quartz. There are more than three depending on where in the world you live, but for now let’s stick to the UK. Now quartz is what we call an abundant mineral (which just means there is loads of it) while the other two minerals may be less so. If your white rock is not quartz, it could be calcite or marble – or perhaps something else.
To find out if you have quartz or not, there are a number of tests that you can perform. Here are the basics which should help you get a mineral ID on quartz samples.
How to Test for Quartz?
Try these tests to make sure your mineral sample is a quartz crystal.
Test for Quartz 1 – Lick It
If you live in an area where salt-based minerals are formed, then these white salt-based minerals could look like quartz. If you lick it and it doesn’t taste salty then you can eliminate those minerals. Halite is the most likely answer if it is salty and white.
Test for Quartz 2 – Scratch It
All minerals have a set hardness. Very few cross the hardness boundary to have mixed hardness. Mercury has a mixed hardness, for example, as it reacts to heat. What doesn’t have mixed hardness is a lump of quartz. In fact, it should always, always have a hardness around 7 on the Mohs hardness scale.
To put that into perspective, talc – the rock used to make talcum powder – is at the bottom with a hardness of 1. Diamonds sit at the top of the Mohs scale, with a hardness of 10. What does this mean for your quartz? That it is extremely dense and solid. You can smash it with a hammer but it takes elbow grease. Some gold panners even crush down quartz to extract potential fine particles of gold from it.
So, to test for a hardness of 7 you must scratch your quartz with things less than that hardness to see if they scratch the quartz rock. If you use a stainless steel knife it should have a hardness around 5.5 or 6. It should not scratch the quartz. However, 5.5 is hard enough to scratch calcite. So if you scratch that rock with a knife and it makes a mark, you can tell it is less hard than quartz and is therefore likely to be a calcite or marble, a morphed form of calcite.
Test for Quartz 3 – Scratch With It
You can also take that piece and attempt to scratch the bottom of a glass or a piece of ceramic. Use something old for this because if it is quartz it will leave a scratch on the object. Any material softer than quartz is unlikely to scratch your ceramic or glass.
If you want to be professional and exact about this (it is a science, after all) then you can invest in a set of real Mohs hardness testing kits. Other minerals leave coloured streaks if you scratch them along a ceramic or slate object. Test kits for this are popular among jewellers. If you regularly buy silver and gold, one of these kits is worthwhile.
Test for Quartz 4 – Look for Bubbles
You can eliminate quartz as a potential mineral ID for any piece of marble or calcite. Simple add some white vinegar to the surface area and look for small, frothy bubbles. Small bubbles indicate that the mineral is made of calcite and is eroding under the vinegar. This test works for the same reasons that marble countertops take extra care and cleaning… calcite and marble are not resistant to acids. Quartz is.
Test for Quartz 5 – Specific Gravity
Each type of mineral has an allocated specific gravity. This is a little more complex. If your quartz has passed each test above then it is probably OK to skip this one. If not, then prepare to do a little math.
To find the specific gravity of a piece of quartz you must first weigh it. You should then pour a cup of water and weigh it. Record both measurements. 1 litre of water weighs 1,000g, which makes it a reasonably easy sum.
Take the rock and put it into the cup, then record how much water is displaced by the addition of the rock by measuring the increase in volume.
Next divide the weight of the dry rock with the increase in volume. You will have your specific gravity by the end. You can use this chart to see if your rock is not quartz. If it is quartz, it should have a specific gravity of 2.65. Calcite is 2.72, just for comparison.
So if your rock is 100g and you put it into 500ml of water and the water increases in volume by 2.65, then you have quartz.
Identifying Other Scottish Crystals and Minerals
Stay tuned to The Stone Circle’s rock and mineral blog to keep up to date with how to test for quartz, calcite, and other minerals. You can follow us on Facebook to get the latest updates or join us on Instagram for the best pics of Scottish crystals, rocks, and minerals. Shop online in our crystal shop in the UK or use our Etsy store if you feel more comfortable.
If you would like further guidance on rock and mineral testing, these mineral testing kits available on Amazon will teach you more.
Where to Buy Scottish Quartz?
You can jump straight to our Scottish Quartz section to browse our full range of quartz crystals. We also sell rough smoky quartz from the Scottish mountains by the 500g for rock tumbling hobbyists and lapidary work. You can read more about quartz on our blog, too.
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