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Identity HelpHelp identifying microminerals in basalt vesicle

29th Jul 2017 18:40 UTCCarlos Santana

Hi friendly Mindaters,

Recently on a visit to Alisitos Beach, Playas de Rosarito, B.C., Mexico, I noticed a rock (either basalt or andesite) that seemed to have weathered zeolites in its vesicles. I took it home, took a hammer to it, and threw the pieces under the microscope. Sure enough, I found well-formed crystals in the interior vugs.

I'm aware that these probably aren't precisely identifiable just by visuals, but I have attached pics in this and the subsequent post. Does anyone have suggestions for tests I could do at home to make progress on identifying these?

The photos in this post are of a cavity measuring 3.2 x 5 mm at the lip, and the zoomed in photo has a fov of 1.2 mm.

The photos of the second specimen, in the following post, are of a cavity measuring 2 x 3 mm, and the zoomed in photo also has a fov of 1.2 mm.

Thank you!

29th Jul 2017 18:41 UTCCarlos Santana

Here are photos from the second specimen.

29th Jul 2017 20:13 UTCGeorg Graf

Hi Carlos,

take a little piece in vinegear. If it fizz, it can be Calcite or Aragonite. - If it fizz not, it can be a Zeolithe, e. g. Natrolite, Skolecite or Mesolite or other.

A further proposal: Look for literature about the place you found the specimens. Maybe there is a description of the occurring minerals available.

Good luck! Georg

29th Jul 2017 20:21 UTCGeorg Graf

Hi again! Are you the musician Carlos Santana, "Black Magic Woman"?

29th Jul 2017 20:23 UTCPaul Brandes 🌟 Manager

Welcome to Mindat, Carlos!

I'm thinking these are tiny Natrolite balls/sprays inside the basalt vesicles. The literature I have from that area says zeolites (Natrolite) were discovered in the Table Mountain area near Rosarito Beach. I'm not sure if these are near where this specimen comes from, but it's worth mentioning. Nonetheless, it is a great find and I bet there are more in the basalts. Georg's advice is good; sacrifice one of the crummier little pieces to vinegar and see if it fizzes.

29th Jul 2017 20:33 UTCWayne Corwin

Carlos

Same area of "Playas de Rosarito, B.C., Mexico" you mentioned, here in Mindat
https://www.mindat.org/gallery.php?loc=277056&min=2947

it also says ""Natrolite is described in the geological literature in the layers of basalt in the Rosarito Beach formation.""

The main page listings>> https://www.mindat.org/loc-277056.html

Keep On Rockin'

Wayne

29th Jul 2017 20:41 UTCAlfredo Petrov Manager

Welcome, Carlos, I hope you have a lot of fun on Mindat, and have the chance to do some more collecting in Rosarito.

Unfortunately, Mindat's species information for that area is pitifully incomplete: https://www.mindat.org/loc-277056.html - so more contributions will be very welcome.

The San Diego Natural History Museum used to have (when I was working there, over 30 years ago) the world's finest collection of Baja California minerals, many of them collected, or purchased from local people, by the legendary Josie Scripps. Now the museum's systematic collection seems to have been dumped or pillaged or disappeared into an ignominous storage somewhere - I'm not sure. Anyway, I remember several nice zeolite specimens, miniatures to small cabinet size, from the ocean cliffs near Rosarito, where they were best collected in early Spring, after winter storms cause bits of cliff to come crashing down.

29th Jul 2017 21:45 UTCMichael Harwell

Hi Carlos, can you post a pic of the rock before you broke it. Or zoom into the part that made you think of bringing it home to break. What made you think to break it open. I have a bunch I want to break open but I need the right hammer equipment and time. But I do collect ones with dimples or ones that just look like something might be inside. Any hints or technique To breaking them. I've tried. It's dangerous. Plus, I don't know what they are so breaking something up into small pieces with dust scares me thus I've waited. But interested with lots of rocks to bust open. Thx

29th Jul 2017 21:59 UTCGary Moldovany

It's not on the mineral list but my first thought on photo # 1 was gonnardite. Looks like a little green prehnite in there too. The second specimen thomsonite?

29th Jul 2017 22:16 UTCCarlos Santana

Thanks for your input, everyone.

Vinegar etched crystals like those on specimen 2, so it seems likely that those are a polymorph of calcium carbonate. Other crystals, like specimen 1 and some grayish crystals I haven't yet photographed did not react with vinegar.

Natrolite is one of my leading guesses as well, but the literature on the area is fairly sparse. Not only does Mindat have little information, but even old publications I was able to requisition through my university had little of use. As Alfredo mentioned, large specimens of Natrolite are known from the area, but I haven't been able to find much scientific literature on what other zeolites might be found in the volcanic rock of northwest Baja.

Michael, I didn't photograph the rock before breaking it, but what clued me in to possible micros was that the some of the vesicles on the surface were lined with a white, translucent mineral. Of course, being on the beach, the surface was worn and rounded, and those white minerals had been weathered down, but that suggested that there might be unweathered versions of the same inside the rock.

As for breaking safely, I do it outdoors with a rock hammer, gloves, and safety glasses, then use an end nipper to trim down smaller pieces. For specimens where the dust is a concern, wear a mask and break the rock in a well-ventilated area.

30th Jul 2017 01:24 UTCDonald B Peck Expert

Carlos, The crystals may be too small for this, but try to get an impression of the shape of the end of a larger one. If it is square in cross section, or nearly so, it is most probably natrolite.

31st Jul 2017 05:11 UTCD Mike Reinke

Michael, from my beach/rock hammering experience, I'd say you need not fear dust. Grinding on the other hand, is dusty and becomes dangerous breathing, but hammering silicates mostly leaves grit, not dust. Eye protection is far more important for the shards of chert, etc... And what volume of hammering are you doing? I handle a few pounds a month, when I have time, never hours a day...I would assume you do the hammering outside, which is naturally well ventilated. It would be very hard on any floor...!

Another Michael

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