KERNITE

Kernite – Na2[B4O6(OH)2].3H2O – is an extremely rare hydrated borate, important as an ore for the manufacture of “chemical borax,” even more important than borax itself, because kernite contains less water than borax. The deposit in the Kramer District (Boron, California, USA) was for many years the only known occurrence of kernite and the most important deposit for the production of “chemical borax.”

Kernite alters to metakernite when heated to temperatures above 100-120°C; a change that is not reversible. In cold water, kernite is slowly soluble, but in hot water it dissolves easily. By dehydration, it alters to tintalconite, forming efflorescences in collector’s pieces: initially, kernite forms a white powder on the surface of the crystals, which develop fractures. Then it becomes opaque and dull, and in extreme cases, the entire kernite crystal turns into white tintalconite powder.

The largest known kernite crystal measured 2.44 x 0.9 x 0.9 m, weighing 3.8 tons. In the Kramer deposit (CA, USA), masses of kernite 9 meters long were found. Kernite has a sweet, metallic taste, but its ingestion is not recommended, although B is not very toxic, very safe.

Since kernite is neither a transparent rock-forming mineral nor a classic opaque ore mineral, there is no reference to it in traditional mineralogy textbooks. The mineral is simply not discussed. Microscopic images of kernite are not available in any of the available literature.

1. Characteristics

Crystal system: Monoclinic prismatic.          

Color: Colorless to white. Light gray.     

Habit: Equigranular crystals, slightly elongated by [100]. Massive. The cleavages simulate, in cleavable masses, a fibrous structure.

Cleavage: {100} perfect, {001} very good, {-102} distinct. Deep striations by [010].

Tenacity:  Flexible and elastic.        

Twinning: On {011}   

Fracture: Splintery.

Mohs Hardness: 2.5

Parting: No.

Streak: White. 

Lustre: Vitreous, silky in fibrous cleavages. 

Diaphaneity: Transparent.           

Density (g/cm³): 1.906

           

2. Geology and Deposits

Kernite is one of several borates found in borate deposits of evaporite sedimentary origin in arid regions, formed from salt lakes.

At the type locality (Rich, Kern county, California, USA) kernite occurs in a layered, metamorphic deposit of borates in shales. It forms the rock known as “kernite-stone”.

 

3. Mineral Associations

It is associated with other borates such as ulexite, tincalconite, inyoite, colemanite, probertite, and borax.

Also with gerstleyite and, more rarely, with realgar.

 

4. Transmitted Light Microscopy

Refraction indices:  nα: 1.454 – 1.455     nβ: 1.472      nγ: 1.487- 1.488

PLANE POLARIZED LIGHT – PPL

Color / Pleochroism: Color.

Relief: Moderate.           

Cleavage: {100} perfect, {001} very good and {-201} distinct.           

Habits: Almost equigranular crystals, slightly elongated by [100]. Massive. Cleavable masses simulate a fibrous structure due to perfect cleavages.

CROSSED POLARIZED LIGHT – XPL

Birefringence and Interference Colors: Maximum birefringence of 0.032, corresponding to strong, intense, and colorful colors up to the end of the second order.  

Extinction: Oblique in relation to the cleavage, between 19 and 38º.

Elongation sign: No information available.            

Twins: On {011}.         

Zoning: No.             

CONVERGENT LIGHT

Character: B(-)          

2V angle: 80º         

Alterations: Dehydration alters it into tintalconite. At temperatures above 100-120ºC, it alters it into metakernite.          

May be confused with: No information available.         

Caption.

5. Reflected Light Microscopy

Reflected light microscopy is clearly not the recommended analytical method for identifying the mineral. There are no opaque minerals that occur associated with the mineral.