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Identity HelpIndian Mesolite? and amethyst geode

10th Apr 2016 16:47 UTCDaniel OKelly

Picked this up cheaply in a rock shop labeled as Mesolite in an amethyst geode. It's obviously an Indian Deccan trap specimen, but is it actually mesolite, or could it be scolecite or another zeolite? Also, I haven't found any pictures of geodes with zeolites on amethyst on mindat or on the jnternet (plenty of zeolites on plain quartz in geodes though). Is this combination unusual?

Thanks,

Dan.

10th Apr 2016 16:48 UTCDaniel OKelly

10th Apr 2016 16:49 UTCDaniel OKelly

11th Apr 2016 19:24 UTCDaniel OKelly

Any views appreciated. Thanks, Dan.

12th Apr 2016 17:17 UTCD. Peck

Dan,

I enlarged the photos in an attempt to look at terminations on the white crystals. Mesolite is orthorhombic (which you probably know) and scolecite is monoclinic with a beta angle of 109^o . I couldn't get a good look, but one or two of the crystals appeared to have a rather rectangular relationship between the termination and the "prism" of the crystal. That would tend to indicate Mesolite. However, two or three out of focus crystals seemed to show the termination not at 90^o, so arguably scolecite. Maybe you can get a better view with a magnifier.

13th Apr 2016 10:55 UTCDaniel OKelly

Thanks Don. I'll try to get some zoomed in and in-focus photos and upload later today. Grateful for your views.

13th Apr 2016 11:21 UTCBen Grguric Expert

If you are prepared to sacrifice a tiny fragment e.g. from the underside of the spray, and you know someone who has access to a petrographic microscope, there is a surefire way of distinguishing mesolite from scolecite. A fragment crushed should break into tiny needles. Place on a glass slide and add a drop of water and examine under crossed polars in the microscope. Mesolite (and natrolite and thompsonite) should give straight extinction (i.e. the needles should go black when parallel with the crosshairs) while scolecite should give inclined extinction, up to 18 degrees rotation from the crosshairs.

Also if there is a gypsum or mica plate on the microscope, scolecite is always length fast, natrolite is always length slow, and mesolite can be length fast or slow depending on the orientation of the needle about its long axis.

13th Apr 2016 22:07 UTCDaniel OKelly

Quality still not wonderful, but a bit more detail of the zeolite spray. I'm still wondering whether it is common to get zeolites on an amethyst matrix. I have seen a couple with Okenite in association but nothing else.

Thanks.

14th Apr 2016 19:24 UTCDaniel OKelly

I've had a look through a magnifier and the terminations do appear to be at 90 degrees, i.e. they are rectangular, so this maybe suggests the identification is correct and is Mesolite. Thank you for the help. My question still remains as to whether Mesolite or Scolecite on amethyst is unusual in Indian specimens compared to geodes with white quartz.

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