Immersion method (mineralogy)

In the immersion method (from the Latin immergere = dip , immerse ) translucent objects in liquids are immersed to the refractive index to determine or estimate the articles.

Action

Liquids with different refractive indices (selection)
liquid	Material (example)	Refractive index n
chloroform	opal	1.45
1,8-cineole	Fused silica	1.46
Tetrachloroethane	Moldavite	1.49
Benzene / toluene	Lapis lazuli	1.50
Trimethylene bromide	Petalite	1.51
Chlorobenzene	Moonstone	1.52
1,2-dibromoethane	Feldspar	1.53
2-nitrotoluene	amethyst	1.54
Xylidine	Scapolite	1.56
N-methylaniline	emerald	1.57
Bromoform	beryl	1.60
Quinoline	topaz	1.62
Polychlorinated naphthalenes	turquoise	1.63
Diiodomethane	Ruby / sapphire	1.74
Diiodomethane, saturated with sulfur	Benitoite	1.78
White phosphorus- sulfur-diiodomethane mixture (weight 8: 1: 1)	Titanite	2.06

An object with an unknown refractive index can be immersed in various liquids with a known refractive index using immersion . If the refractive indices of the object and the liquid match, the contours of the immersed object disappear because the light rays are no longer refracted at the interfaces .

If facets and edges are visible, the actual refractive index of the material can be estimated as follows:

Contour and edges	Refractive index in relation to the liquid
White outline / black edges	smaller
Blurred contour and edges	equal
Black outline / white edges	greater

The wider the contour, the greater the deviation between the refractive indices of the object and the liquid.

Areas of application

Identification of gemstones

The method can with certain heavy liquids are used to gemstones to identify.

For example, rubies or sapphires can be immersed in diiodomethane . The main component of ruby and sapphire is aluminum oxide . Its refractive index is close to that of diiodomethane . As a result, the contours of these stones disappear almost completely after immersion. Gemstones made from a different material, on the other hand, remain easily recognizable after immersion in the same liquid. ${\ displaystyle n = 1 {,} 76}$ ${\ displaystyle n = 1 {,} 74}$

Emeralds have an index of refraction of . You can be identified by N-methylaniline . ${\ displaystyle n = 1 {,} 57}$

This process works particularly well with cut gemstones. Because after immersion, the reflexes on the facets of the cut disappear .

Birefringence

Birefringent objects can also be identified as the visible edges of the respective object change when it is rotated in the liquid.

literature

CRC Handbook of Chemistry and Physics , Liquids for Index by Immersion Method

Web links

Determination of the refraction of light

Individual evidence

^ Walter Schumann: Precious stones and gemstones (= BLV determination book. 17). 4th revised edition. BLV Verlagsgesellschaft, Munich et al. 1984, ISBN 3-405-12488-3 , chapter light refraction .

[1] Walter Schumann: Precious stones and gemstones (= BLV determination book. 17). 4th revised edition. BLV Verlagsgesellschaft, Munich et al. 1984, ISBN 3-405-12488-3 , chapter light refraction .