Patró d'interferència conoscòpica: diferència entre les revisions
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An interference figure produced looking straight down or close to the optic axis of a uniaxial mineral will show a characteristic [[Maltese cross|"Maltese" cross]] shape to its isogyres. If you are looking perfectly down the optic axis, the pattern will remain completely unchanging as the stage is rotated. However, if the viewing angle is slightly away from the optic axis, the centre of the cross will revolve/orbit around the central point as the stage is rotated. The form of the cross will stay constant as it moves.
[[File:Biaxial interference figures.jpg|thumb|center|upright=2.5|<center>Possibles figures d'interferència per a un mineral biaxial amb una àmplia 2V, vist al llarg d'un dels dos eixos òptics. La forma corbada de l'isogir (banda fosca) és característica dels minerals biaxials, tot i que el grau de curvatura canvia a mesura que fem girar el microscopi, i el patró s'assembla en algunes orientacions al patró de
The optic axis figure of a biaxial mineral is more complex. One or two curved isogyres (sometimes called "brushes") will be visible, one of which will have its point of maximum curvature perfectly centred. (The figure shows an example with a single isogyre visible.) If two isogyres are visible, they will be positioned back-to-back. Rotating the stage will cause the isogyres to move and change shape strikingly - moving from a position where the isogyres curve smoothly and are widely separated at their closest point, then gradually becoming more tightly curved/squarer at their midpoints as they approach each other (a second isogyre appearing from out of the field of view if it was absent before), then merging to form a maltese cross pattern very much like that of a uniaxial mineral. Continuing to rotate the stage will cause the isogyres to separate again - but into the opposite quadrants to where they were previously - then meet again, then separate again into their original quadrants, and so on. The isogyres will touch each other four times in one 360 degree revolution, with each time corresponding to one of the [[extinction position]]s seen in normal cross polarised light.
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