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Opaline Silica might just be the best thing since sliced bread. It is a granular absorbent containing hydrated silica (Amorphous Opaline Silica) and bentonite brought to us by the same great people at Oil-Dri (Pure-Flo, Agsorb, etc) who mine some of the industry’s favorite filtration media such as B80.

“Diatomaceous shale is altered rock primarily made from the fossilized remains of tiny, aquatic organisms called diatoms, along with minor amounts of clay minerals. Over millions of years, these small organisms collected in the sediments of rivers, streams, lakes, and oceans, and then became deeply buried and altered into hydrous opaline aluminosilicates. Diatomaceous shale is very fine and porous.” -OilDri

“In the Gusev crater of Mars, the Mars Exploration Rover Spirit inadvertently discovered opaline silica. One of its wheels had earlier become immobilized and thus was effectively trenching the Martian regolith as it dragged behind the traversing rover. Later analysis showed that the silica was evidence for hydrothermal conditions.”  Ruff, S. W., et al. (2011)

What is it:

“[F]rom Taft, California is a Hydrous Aluminosilcate (SIC) mineral. Its low bulk density and high absorptivity allows higher liquid holding capacity. Our mineral processing maximizes the granule’s micropore space. AGSORB® heat treatments impart a hard, inert granule with a high resistance to attrition. The unique properties of this mineral make it harder in its natural state than other RVM products.”  -OilDri

Chemical composition by weight:

80% SiO2, 9% Al2O3, 8% H20, 2% Fe2O3, 1% Other salts

RVM (Regular Volatile Material)

LVM (Low Volatile Material)

How is it different from other filtration media?

The two biggest differences from the processor’s standpoint are ease-of-use and required operating pressure. Opaline silica is granular and not a cumbersome powder, so you won’t make a huge mess every time you pack a filter. For that same reason, you no longer have to worry about inhaling dust (and hydrated silica does not cause silicosis). You don’t need to pre-bake your filtration media,* you don’t need to pre-wet it either. You don’t need to pack it down, and you don’t need a DE/Celite layer, just a 5-micron filtration paper, and retention ring. 

However, according to extraction guru Photon Noir “depth filtration is important to achieve stringent particle removal and reasonably fast flow. This can be achieved using a strong screen supporting the media’s weight above some cotton wadding, filling the space between the screen and another sheet of screen over the outlet hole… not packed too tight, but tightly fitting around the sides, where dust would like to channel”.

He also recommends baking your media before use but when we did that we experienced lower yields. MediaBros recommends not baking your media prior to use.

What are its capabilities and limitations?

This is not the best filtration media for water-clear. However, when used properly it can remove a bulk of your color. Water clear can be achieved in some instances depending on the starting material and whether or not you are recirculating.

How do I use it?

  1. Do not bake the filtration material before use*
  2. 5-micron paper screen at the bottom of your column with retention ring
  3. Add 100-200 grams of Opaline Silica per 1lb of starting material(An 8”x3” column can hold about 800 grams of opaline silica) (You can put your filtration media in a sock for easy CRC swaps)
  4. Partially close inlet and outlet valves on CRC to control flow. Keep flow at 2-4 LPM.
  5. Run the system with cold solvent at 5:1 ratio or higher and slowly pass the solution through the CRC. You may need to add some pressure but nowhere near as much as with clays/powders.

Where can I get it?

RVM is mined in Taft, California by Oil-Dri/Agsorb and it comes in 3 different mesh sizes. For processing, we will be using either the 16/30 or 24/48 mesh size To purchase from OilDri, you need to set up an account and order 1000lbs at a time. If you’d like to try a smaller amount you can purchase from multiple sources such as MediaBros or (cheapest option).  Oil-Dri makes lots of products that look very similar, make sure you’re getting “RVM” from their mine in Taft, California AKA “RVM-T”

Make sure to steer clear of any absorbents that contain “cristobalite, a crystalline form of silica that is listed as a class 1 carcinogen and is very common in clay deposits, especially bentonite, so it is good to warn folks not to just go around trying any old high silica clay media” – Photon Noir


 The high flow rate of the opaline silica allows you to set up an AODD (air-operated dual-diaphragm) pump to pump liquid butane (or another hydrocarbon) from your collection vessel back through your CRC (color remediation cartridge) over and over until the solution reaches the desired color. On large (multi-column) batches you can recirculate while you recover.

 Make sure to order a pump with PTFE diaphragms. The one I picked out has ½” inlet and outlets and a max operating pressure of 100PSI which is 2x-3x what our system will ever reach with opaline silica. Here is a nice option, and another  and Sambo Creek makes some that will work as well. Make sure to get the model with metal housing. These pumps run at about 12-15pgm which is higher than our ideal flow of 1GPM, but you can just keep passing the solution over your material until the desired results are obtained.


*The RVM is 9% H2O by weight and baking might help pull color, however, I tried baking media before use and saw diminished yield. Media Bros suggests not baking while Photon Noir suggests baking, these two are great sources for information and in this instance, they have conflicting views. I encourage you to try both and report back with your findings. 

On that note, shoutouts to:

 Photon Noir, Media Bros, Tom from OilDri, Cyclopath,  Dred_Pirate, and ColombiaBeneficial.

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