Hydromagnesite / Huntite

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Product Description
Benefits & Application Details



Securoc C10 and Securoc D10 products are different blends of two minerals: Huntite and Hydromagnesite

Huntite particles have a platy morphology and the particles are usually about 1 μm or less in diameter, much smaller than hydromagnesite particles. It has the following chemical formula and thermally decomposes between about 450°C and 750°C in two stages, releasing only carbon dioxide, leaving a solid residue of magnesium oxide and calcium oxide:  Mg3Ca(CO3)4 → 3MgO + CaO + 4CO2

The solid residue is called “char” and is critical to obtain smoke suppression . Char coming from Huntite has better mechanical properties than char generated by the thermal decomposition of hydromagnesite (which only consists of MgO – see below).


Property Value Unit
Hardness (Mohs) 1-2 [-]
Refractive index 1.62 [-]
Density 2.7 [kg/ dm3]


Natural hydromagnesite particles have a “blocky” morphology and once processed the majority of the particles are usually between 1 and 10 μm in diameter depending on the processing. 

It thermally decomposes between about 220°C and 550°C in two stages, initially releasing water then carbon dioxide, leaving a solid residue of magnesium oxide:  Mg5(CO3)4(OH)2·4H2O → 5MgO + 4CO2 + 5H2O


Property Value Unit
Hardness (Mohs) 3.5 [-]
Refractive index 1.54 [-]
Density 2.2 [kg/ dm3]


Basic product (mineral blend) properties

Property C10 D10 Unit
Moisture 0.6 0.6 [%]
pH 10 10 [-]
Hardness (Mohs) 2 – 3 2-3 [-]
Refractive index 1.61 – 1.64 1.61-1.64 [-]
Colour (D65/ 10°) L* 98 98 [-]
Ry 93 93 [-]
Density 2.5 2.6 [kg/dm3]


Securoc products overview

Product Grade D50



[g/ 100 g]

Surface treatment
Securoc C10 3 57
C10 F11.0 3 57 1% stearic acid
D10 3 57
D10 F12.0 3 57 2% stearic acid

Securoc products (mixture of huntite and hydromagnesite) are mostly used as a flame retardant or fire retardant additive in polymers.


Natural mixtures of Hydro-magnesite (Mg5(CO3)4(OH)2·4H2O) and Huntite (Mg3Ca(CO3)4) – products called Securoc C or D (depending on the ratio of the 2) – Securoc C and D also available with stearic acid treatment.

Flame retardant fillers are effective in the initial stage of a fire and depending on the mineral retard the fire in different ways:

  • ATH and Hydromagnesite  (present in Securoc product) are hydrated products and incorporation of these minerals into a formulation reduces the fire-risk as the substances release water upon an endothermic thermal decomposition (ATH at 200°C and hydromagnesite at around 220°C), hereby lowering the rate of heat-release (heat being one of the “corners of the fire-triangle”). Mineral mixtures of Hydromagnesite and Huntite further reduce the fire-risk as at higher temperatures they further decompose forming a char-layer with a platy structure on top of the combustible material, hereby isolating the fuel-source (another “corner of the fire-triangle”)  from the flame and consequently retard the fire.  The char-layer also reduces the release of smoke from the fire (smoke suppression).  The mechanical properties of the char-layer are limited (but stronger with an increasing amount of huntite) and at some point the layers will collapse and the fire will propagate again


In Sealants and Adhesives Securoc products can have an impact on the rheology profile of the sealant and/or adhesive because of the lamellar morphology of the huntite and its fairly high oil absorption (compared to other mineral fillers). When applying shear, the lamellar particles will align and provide a low viscosity. When shear is removed, the lamellar particles lose their orientation and cause the viscosity to increase above the level expected when the particles had a more regular shape.

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