Loupewise / Reference / Sphalerite
Properties Refractometer Key Tests Sphalerite has a specific gravity of 4.09 and a refractive index of 2.369–2.371, with a Mohs hardness of 3.5–4.0. It is singly refractive.
Physical & Optical Properties
RI Range 2.369–2.371
SG Range 3.90–4.10
SG Typical 4.09
Hardness (Mohs) 3.5–4
Crystal System Cubic
Optic Character SR (Singly Refractive)
Dispersion 0.156
Fluorescence LW Variable
Fluorescence SW Variable
Chelsea Filter Inert
Pleochroism None
Colors Yellow Orange, Brown, Red Pink, Green, Black
Species Sphalerite
Measured with a polariscope , a refractometer , a hydrostatic balance , a Chelsea filter , a UV torch , a loupe , a darkfield loupe and a spectroscope — step-by-step for each.
Through the refractometer
Sphalerite
no reading — over the limit
1.40
1.45
1.50
1.55
1.60
1.65
1.70
1.75
1.80
REFRACTIVE INDEX
DO Read the scale from bottom to top, then look for the liquid’s own faint line near the top.
SEE The field stays dark, with one faint line near 1.81 that does not move when you change stones.
MEANS Over the limit — this stone’s index is above the contact liquid’s own, so the liquid is the last thing the instrument can still see. That faint line is your proof the instrument is working rather than dead. It is a RESULT: it eliminates every species below 1.81 in one observation. A field dark with NO line means something else has gone wrong.
Drawn from the refractive index above, on a 1.40–1.81 scale.
How to take this reading .
Through the polariscope
Sphalerite
Dark throughout (SR)
0°
45°
90°
135°
ROTATION BETWEEN CROSSED POLARS
Sphalerite stays dark through the whole rotation. That is singly refractive: there is no second
ray to rotate the plane of vibration back into the analyser.
Drawn from the optic character and transparency above.
A polariscope separates singly refractive, doubly refractive and aggregate;
the optic sign needs a conoscope.
How to take this reading .
Specific gravity, and what it rules out
Sphalerite
SG 3.90–4.10
WHERE IT SITS, AND WHAT ELSE IS THERE
1.0
2.0
3.0
4.0
5.0
SPECIFIC GRAVITY
15 other species in the table overlap this range, so a reading here narrows the field to 16 rather than
naming the stone. Combine it with a refractive index to separate what is left.
Drawn from the specific-gravity range above, against
every other species in the table.
How to take this reading .
Through the dichroscope
Sphalerite
One colour (no pleochroism)
IDENTICAL AT EVERY ANGLE
Sphalerite shows no pleochroism, so both windows match at every orientation — turning the instrument
changes nothing. That is a real negative result, and the reason it is worth knowing is below.
Drawn from the pleochroism above. Two windows that match
mean either no pleochroism or the wrong angle — turn the instrument to tell.
How the dichroscope compares .
Key Differentiators
Extraordinarily high dispersion Low hardness Perfect dodecahedral cleavage
Identifying a sphalerite? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
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Studying for the GIA, FGA, or FEEG practical? Sphalerite is one of the 132 species in Loupewise’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
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