Boulder Opal Rough

Boulder Opal Rough
boulder opal rough and specimens

Boulder Opal Rough

Boulder opal rough is opal taken straight from the mine. It requires some skillful cutting and polishing to remove the excess ironstone and a little luck to split or slice in the right place.

So far this type of opal comes exclusively from Australia and the Queensland fields in particular’. It has a dark to black body tone as defined by the body tone scale for opal classification. Actually, this is another form of black opal because of its dark opaque appearance

Boulder opal comes in brown hard ironstone

Boulder opal rough is opal still attached to the mother rock, in this case, ironstone. The opal mostly runs in seams inside the ironstone and is often unseen until the opal cutter makes a cut into the rock.

Some boulder opal is discovered by cracking open a piece of ironstone boulder to see whats inside. The opal seam sometimes splits the boulder in half and this can often result in mirror pairs of opals called ‘split faces’. These are often cut and shaped to be used as matching earrings.

Matrix is another kind of opal. This stone, rather than appearing as seams in the ironstone shows up as flecks of opal color scattered through a piece of ironstone. This type of boulder opal rough is often used for making beads which look spectacular.

Cutting and Polishing this unique opal

Cutting and polishing this stone is a specialized form of opal cutting. It can be a little messy because the boulder ironstone can stain your clothes if you are not careful so it’s good to have appropriate spray control and select machinery that allows the water to drain away rather than run in a muddy ‘soup’ as was the old way of doing it.

The rough boulder opals are cut using a diamond blade and then cleaned up and shaped on an opal grinding wheel. Polishing is done with sandpapers and a leather lap or felt wheel with cerium oxide paste to get the final polish. Rubberized diamond wheels are also used very successfully for boulder opal cutting but more details of this can be found in our section on opal cutting.

Many collectors keep polished and unpolished boulder opals as specimens or conversation pieces. The dark brown ironstone is a fantastic setting to display opal in and many jewelry stores that have opal jewelry will have a specimen to drape their jewelry over because it’s a great way to see the product from its original state to being able to be worn.

6 thoughts on “Boulder Opal Rough

  1. Boulder opal is probably my favourite….what’s yours? 🙂

    1. Yup, i agree Anita. its the most original of all the opals and with all the synthetics around nowadays, its much easier to tell that its a natural stone. Peter

  2. May I ask you if there are any special care instruction for the boulder rough opals? Do the need to be soaked in water or have baby oil applied to them until you cut them???

    1. Sherri, so sorry for late reply. our alert system was faulty. no need to worry about any special treatment for boulder opal. just dont break it against a wall or rock or they could shatter like most gemstones. hope that helps, Peter

  3. Hello!I like the lot Boulder Opal Rough 8016 beacose this boulder opals have big size enough.I plan pendant and bracelet.Can you halp me with catting and polishing .Can you tell me about new sises after treatment this Boulder Opal Rough..And how much will cost to make pendant and bracelet with silver.Pendant like this bracelet like this but biger Sory for my english.Svetlana

    1. Svetlana, pleased to help you. Your english is fine. Much better than my Russian. i think all i can say is goodbye in Russian. Do you mean that you have a piece of boulder opal already that you would like to learn how to cut and polish? if so, please email and send me a picture. If you want to buy a set of boulder opals and have them set, that is different. first tell me a bit more about it. thanks Svetlana. how’s the weather in Russia. Its very hot here in australia. best wishes, Peter

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