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G-200 Feldspar

Alternate Names: G200 Feldspar, G200 Spar, G 200 Spar, G 200, G 200 Feldspar

Oxide Analysis Formula
CaO 0.80% 0.08
MgO 0.05% 0.01
K2O 10.80% 0.64
Na2O 3.10% 0.28
Al2O3 18.50% 1.01
SiO2 66.30% 6.12
Fe2O3 0.08% 0.00
Oxide Weight 553.04
Formula Weight 553.87


G-200 Feldspar was a high quality potassium / sodium / calcium aluminum silicate ground to 200 mesh for ceramic applications. Carefully beneficiated and controlled for quality, G-200 offered high potash content and low iron oxide per unit of alumina. It was mined in Monticello, GA.

September 2013: The trials at the Feldspar Corporation failed. After 57 years of operations, the Monticello plant was targeted for closure on December 31, 2013 because there was no additional available potassium feldspar ore in the area. However a G200 equivalent material imported from Spain was slated for availability in bulk bags and 25 kg bags (for around $350-450 ton plus shipping). These products were to be sold from Savannah, GA or Newark, NJ (90 days lead time for orders).

2013: Laguna Clay markets a 3:7 blend of Minspar:G200HP that they call "Old Blend" and it is a close equivalent of the old G200. This is because HP is higher in K2O and lower in CaO than G200 (other oxides are the same) and Minspar is the opposite; so they are a natural mix to duplicate G200. Laguna also sells the new HP material and refers to it as "New Potash".

Jan 2013: Data sheet from Imerys had the following comparison (we have added Minspar):

G200 G200 HP G200 SP Minspar200
SiO2 (%) 66.3 66.0 65.5 68.8
Al2O3 (%) 18.5 18.3 18.8. 18.2
Fe2O3 (%) 0.08 .09 .08 .07
K2O (%) 10.8 14.2 10.7 4.1
Na2O (%) 3.1 0.9 3.8 6.5
CaO (%) 0.8 0.3 0.8 1.5
The surface areas and particle sizes are the same.

December 2012: The Feldspar Corporation in Spruce Pine will be conducting trials to produce a potassium feldspar of similar quality to the Monticello material (because the ore body in Monticello is almost gone).

August 2009: The Feldspar Corporation has traditionally blended sodium feldspar from Spruce Pine, NC with potassium feldspar from Monticello, GA. This was done in an effort to match the chemistry from a depleted mine. However this material is being replaced by G-200HP. It is higher in potassium and alkali levels because the blending practice is being stopped by Imerys. They are recommending a 3:7 blend of sodium feldspar (Minspar 200) with the new G-200HP feldspar to match G200. Kona F4 Feldspar has the same chemistry as Minspar but its mine is closing.

Related Information

Old Blend Feldspar. What is that?

Laguna Clay sells a substitute for the no-longer-available G200 feldspar. G200 HP is higher in K2O and lower in CaO than G200, Minspar is an ideal addition since it's K2O is much lower and CaO much higher. A 7:3 G200HP:Minspar mix produces a chemistry that is remarkably close (on paper) to G200. They label this blend "Old Blend". They also list a product called "New Potash" in their pricelist, that is G200 HP.

Custer feldspar vs. G200 feldspar

This is a melt fluidity test fired to cone 10. By themselves, feldspar melts surprisingly less than you might think at cone 10.

Melt flow tester used to compare feldspars

Fired to cone 10 oxidation. Although feldspar is a key melter in high and medium temperature glazes, by itself it does not melt as much as one might expect in this GLFL test. The Montana materials on the right are not commercially available, they were being evaluated for viability.


Materials Kingman Feldspar
Materials G200 HP Feldspar
Materials MC 200K Feldspar
Materials Minspar 200
Materials F-4 Feldspar
Materials G-200 EU Feldspar
Materials G200 Old Blend Feldspar
Materials Chesterfield Feldspar
Materials F-20 Feldspar
Materials G-20 Feldspar
Materials Custer Feldspar
Materials NC-4 Feldspar
Materials Sil-o-spar
Materials SP-G Feldspar
Materials Potash Feldspar
Materials Mahavir Potash Feldspar
Typecodes Feldspar
The most common source of fluxes for high and medium temperature glazes and bodies.


Apparent Viscosity (cps)13.3
Bulk Density lbs/cu. ft. (Packed)62 loose, 74 packed
Sieve Analysis Dry+200 mesh: 0.5% +325 mesh: 5.0%
Surface Area (m2/gm)1.21

By Tony Hansen

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