Send the brief to the mineral the formula already uses. If the sheet says calcium carbonate, the purchase is a carbonate grade: cut, brightness where you measure it, moisture and packing, on the calcium carbonate line. If the sheet says silica flour or a silica extender, the purchase is a silica cut: particle size, iron where colour or chemistry cares, moisture and packing, on specialty silicas. If the mineral is still unknown, stop guessing and use industrial fillers, with the process tests written out. The comparison CaCO3 filler vs silica filler is a routing decision. It is not a licence to swap the two powders because both can be white and both can be fine.
Plastics and coatings are where the mix-up is most expensive, because both industries buy both minerals, often in the same plant, for different formulas. A compound approved on carbonate and a mill base approved on silica can share a warehouse and still need two contracts. Read mineral fillers for plastics and paints if you are still describing the process rather than the mineral. When you know which file is yours, send it through the trade inquiry.
What buyers mean by the two fillers
Calcium carbonate filler means a CaCO3 grade ground or precipitated for use in a compound, a paint, a paper or a related process. Buyers shorten it to CaCO3, GCC when it is ground from stone, and PCC when it is precipitated. Those last two are different manufacturing routes. A plant that distinguishes them should say so. The note on ground versus precipitated carbonate is the place for that choice. This article only needs you to recognise that both are carbonate, and that carbonate is not silica.
Silica filler, on this desk, means a mineral silica flour or a tight silica cut used as an extender or a functional filler. It is a specialty silica grade. It is not fumed silica and not a synthetic precipitated silica. If the formula names those synthetic grades, write the name in full so a ground flour is not offered against them. Iron and the cut are the usual controls. A bulk silica sand for a glass furnace is not this product either. Sand in a hold is a different contract.
Buyers say "filler" when they mean the cheaper powder in the formula, and they say it for both minerals. That habit is why a carbonate specification gets emailed to a silica supplier and a silica residue gets emailed to a carbonate quarry. The mineral name on the approved formula is the correction. Colour, fineness and a similar bag do not override it.
The decision, and where each brief goes
Make the decision in this order.
- The document in front of you names calcium carbonate, CaCO3, GCC or PCC. Send calcium carbonate. If the plant cares whether it is ground or precipitated, say which, and use the GCC versus PCC note so that choice is explicit. Do not also ask for a silica price "to compare" unless a second formula actually uses silica.
- The document names silica flour, silica extender, or a silica cut with a residue or a d50. Send specialty silicas. Include iron if the plant controls it. Do not translate the sheet into carbonate because carbonate is the more common filler in plastics.
- The document says mineral filler, extender or "white powder" and the plant cannot yet say which mineral the approval used. Send industrial fillers and the process note beside it. Ask the plant before you ask for a price. We would rather return a question than ship the wrong mineral into an approved formula.
- The plant wants both, in two products. Open two inquiries. Two offers, two certificates, two packing lists.
A unit price does not decide the mineral. A lower figure on the wrong powder is not a saving if the line has to be reformulated, if a wear part suffers, or if a colour match fails. We will not publish a performance delta between the two minerals. Your plant already measured the one it approved. Send that mineral.
Specifications each brief should carry
None of these figures is a standing grade on our side. You request them. The lot confirms them. We do not print a d50, a purity, a brightness or an iron level as a fact of "the" carbonate or "the" silica.
For a calcium carbonate filler, ask for the items the plant already uses.
- Ground or precipitated, if the formula distinguishes them.
- Particle size the way the lab measures it: d50 with a method, residue on a named sieve, or a top size.
- Brightness or whiteness with the method, when the compound or the paint is sensitive to it. "White" is not a method.
- Moisture, and where it is measured.
- Any surface treatment the compound requires, named as a requirement. An untreated stone will not become a treated grade in the invoice description.
For a silica filler, ask for a different short list.
- The cut, again with a method or a named sieve. There is no published mesh to order from.
- Iron, as a ceiling, when colour or a chemical limit depends on it. State Fe2O3 unless your method says otherwise.
- SiO2, if you hold a floor.
- Moisture.
- Brightness only if this silica use measures it. Many silica briefs are iron and cut, not a brightness contest with carbonate.
Oil absorption sits on either brief when a paint mill uses it to judge binder demand. Send the method. A carbonate oil absorption and a silica oil absorption are results on two minerals. They are not a conversion factor between them.
Do not copy one mineral's sheet onto the other and change the title. A brightness target written for a carbonate paint grade is not automatically a silica specification. An iron ceiling written for a silica flour is not automatically a carbonate specification. Each contract lists the tests that mineral will be rejected on.
How plastics use each mineral
In many polyolefin and PVC compounds, calcium carbonate is the filler the formula was built on. The plant uses it for volume and cost, and it judges the grade on cut, dispersion, moisture and, in white or natural compounds, colour. A ground carbonate and a precipitated carbonate are not interchangeable just because both are CaCO3. If your approval names one route, keep it. That choice is a carbonate question, handled on the carbonate line, not a reason to wander into silica.
Silica enters a plastics compound when the approval says silica. Plants that have run both minerals do not treat the swap as a purchasing detail. The silica is a harder mineral. Screws, barrels and other wear surfaces see that difference over a campaign. Impact, surface and dispersion were measured on the approved powder. We will not quote a wear percentage or a mechanical uplift. If your process engineer says the compound is carbonate, the silica offer is the wrong brief even when the cut numbers look close.
Misfires in plastics are repetitive. A buyer sends a carbonate grade name and asks for "the silica equivalent" at a finer price. There is no equivalent until the plant reformulates and reapproves. A compounder runs a silica trial in a line whose stabiliser and lubricant package was set for carbonate, then blames the lot for a result the package was never asked to support. A third buyer keeps one filler item code in the ERP for both minerals and wonders why certificates do not match the last delivery. Split the item codes when you split the contracts.
Masterbatch is the same logic at a higher loading. The carrier, the cut and the mineral have to match the approval. A whiter carbonate does not replace a silica the masterbatch was built on, and a low-iron silica does not replace a carbonate the let-down was built on. State the loading only so we understand the process. The purchase is still the mineral and the cut.
How coatings use each mineral
Paints use both powders as extenders, and they use them for different reasons on different formulas. Carbonate is the usual volume extender when the formula says carbonate. The mill watches cut, oil absorption, brightness and whether the gloss or the sheen still lands. Silica is in the formula when that plant wants the film behaviour it associates with silica, often discussed as hardness, scrub or chemical resistance. Those are the plant's words for why the mineral is there. They are not numbers we will invent, and they are not a ranking you can buy off a data sheet without the rest of the formula.
Acid exposure is a plain chemical difference you can use without a performance claim. Calcium carbonate is a carbonate. It reacts with acids. A formula that sees acid, or a test that includes acid, was either built to live with that or it was built on a mineral that does not react the same way. Silica is the mineral those formulas often specify for that reason. If your coating sees acid and the current approval is carbonate, that is a formulation fact to confirm with the plant, not a prompt for us to swap in silica quietly. If the approval is already silica, do not "improve" it with carbonate because the carbonate brightness looks easier to talk about.
Coatings misfires mirror the plastics ones. A decorative paint buyer sends a brightness figure, no method, no mineral, and asks which filler is whiter. We cannot answer with a catalogue number, and whiteness does not identify the mineral. An industrial coating buyer has a silica in the anticorrosive or the topcoat and asks for carbonate "of the same fineness" to simplify the raw-material list. Fineness was never the only reason the silica was there. A third buyer trials both minerals in one batch kettle without telling the contract which result will be the specification. The trial can be useful. The purchase order has to follow the result, not precede it.
Paper and adhesives sometimes sit beside these uses. Name them if they are the real process. A paper carbonate grade and a paint carbonate grade can differ in cut and brightness target. A paper filler inquiry sent as "same as our paint carbonate" needs the paper tests, not an assumption.
Packing and cargo
Both fillers usually travel in big bags, often in containers. That shared packing is one reason the products get mixed up. The bag does not identify the mineral. Marks do. Every bag and every line on the packing list should say the mineral and the grade reference, not the word filler alone.
Ask each plant how it empties the bag. A carbonate line and a silica line in the same factory can have different liners, different spout fittings and different moisture worries. Silica flour and a fine carbonate both cake if the container sweats and the liner is missing. They still need separate marks so a sweaty container is not also a mixed container.
Bulk is possible for either mineral when the grade and the volume allow clean handling and the receiver can take powder without bags. It is agreed per lot. The 5,000 to 30,000 tonne bracket used for industrial bulk silica sand is not the default parcel for either filler. A filler programme of a few hundred tonnes in containers is a normal start. Growing it into bulk is a new check on contamination, moisture and sampling.
Do not ship a carbonate lot and a silica lot under one description to "fill the box". Two grades in one container are acceptable only with separate marks, separate counts and separate certificates. One sample pulled from a random bag then describes nothing. Weight is by weighbridge against the packing list. If you later move one of the minerals into a hold, the weight method, the previous-cargo rule and the Incoterm all get rewritten for that mineral alone.
Documents, inspection and Incoterms
Each mineral carries its own document set, even on the same day to the same port. Invoice, packing list, transport document, certificate of origin from the competent Algerian chamber, weight certificate, and a certificate of analysis. The analysis for carbonate reports the cut and any brightness or moisture the contract named, plus ground or precipitated if that was contractual. The analysis for silica reports the cut and any iron, moisture or SiO2 the contract named. A safety data sheet follows the destination's rule for that product. One sheet with the title changed is not two certificates.
Inspect before stuffing, with the inspector named in the contract. Sample the mineral you are buying, from the stream or from bags identified by mark. A reserve sample of carbonate does not explain a later silica complaint, and the reverse is true as well. If both minerals move in one week, label the seals with the grade reference before anyone leaves the warehouse.
Incoterms 2020, with a named place. FCA at an agreed point in Algeria fits bags and containers for both fillers. FOB at a named load port fits a parcel that is actually loaded on a vessel, with freight and insurance on the buyer. CFR means we arrange freight to your named port and you insure. CIF adds insurance we place, and the certificate joins the papers. Choose the term per shipment. A carbonate sold FCA and a silica sold CIF can both be correct in the same month. They are not one blended delivery.
Payment follows the Algerian bank domiciliation on export proceeds. Discuss it while the grade is still being qualified, not after a vessel is waiting on a specification nobody wrote down.
How the Algerian lot is qualified
Carbonate supply and silica supply are qualified separately. A producer who can grind a limestone is not assumed to be a producer who can make a silica flour, even when both powders end up in big bags. We match the brief to the installation that makes that mineral, at that cut, in that pack.
For carbonate, the questions are the route if you need ground or precipitated, the cut, brightness if you measure it, moisture, and packing. For silica, the questions are the cut, the iron ceiling if you set one, moisture, and packing. Export formalities that apply to the product are checked before the offer is firm. If the lot cannot meet the requested cut or the requested iron or brightness method, we say so. We do not relabel the other mineral as a substitute.
A trial lot is appropriate when the plant has not run this source. Keep the trial inside one mineral. A successful carbonate trial qualifies that carbonate grade. It says nothing about silica. Record the method and the result, and cite them on the next order. If the trial convinces the plant to change minerals, that is a new approval and a new inquiry, not an amendment to the old certificate.
What to send
One mineral per inquiry.
- The mineral in words: calcium carbonate, or silica flour. Add GCC or PCC if the carbonate route matters. Add "unknown" if it is unknown, and then use the fillers file rather than guessing.
- The process: plastic, masterbatch, paint, or the other use.
- The cut as a target, with method. For carbonate, brightness method if needed. For silica, iron ceiling if needed. Moisture. Oil absorption method if the mill uses it.
- Tonnes, bags the plant can empty, destination, Incoterm with a named place, window, and the documents and inspector you require.
Attach the current approval's mineral name if you have it. A formula page with the filler line visible saves a week of the wrong sample.
Our formula says mineral filler and nothing else. Which brief is it?
It is incomplete. Ask the plant which powder was approved, or which tests a new powder must pass, and send industrial fillers with those tests while the mineral is open. Do not let a supplier choose carbonate or silica for you because one of them is easier to offer this month. When the plant answers, move the file to calcium carbonate or to specialty silicas and close the generic one.
Can carbonate and silica share a trial?
They can share a week in the lab. They should not share a purchase order. Run them as two named samples, with two cuts, two certificates and two packing marks, and decide afterwards which approval you are buying. A kettle that contains both, and a contract that names neither, leaves a complaint with no grade to point at. If the trial is only a price exercise, you do not need a production lot of the mineral you have not approved.
The plant wants whiteness. Does that decide the mineral?
Whiteness decides a target on the mineral you already chose. It does not choose between carbonate and silica. Send the method and the figure you need, on the mineral the formula names. A higher reading on the wrong mineral is still the wrong mineral. If you have no mineral yet, say that the selection criterion includes a brightness method, and qualify candidates as separate grades rather than as one "white filler".
We were told silica is harder. Is that a reason to switch?
It is a reason to ask the process engineer whether the approval used silica for that hardness, or used carbonate and would be hurt by a harder particle. It is not, by itself, a purchasing instruction. We will not attach a wear number or a film-life number to either grade. If the plant wants silica because the duty needs it, send the silica brief. If the plant is happy on carbonate, send the carbonate brief. A switch is a reformulation.
Where does ground carbonate versus precipitated carbonate get decided?
On the carbonate line, not in a comparison with silica. Say GCC or PCC if you know which route the formula uses, and read the note written for that choice. Precipitated and ground carbonates are both CaCO3 and both are not silica. Choosing between them does not open a silica inquiry. Choosing silica does not get you a precipitated carbonate under another name.
What do you want in the first message?
The mineral or a clear statement that it is unknown, the process, the cut as a target, any brightness or iron limit you will enforce, the tonnes, the bag, the destination and the Incoterm with a place. That is enough to put the file on calcium carbonate, on specialty silica, or on industrial fillers while the mineral is still open. A price request without those items comes back as questions. Send the message from the buyer inquiry so the trading desk sees one brief instead of a chain of forwards.