🔎 UNIDENTIFIED what kind of basalt is this?

[rockcollect]

I collect basalts because they have cool features in them. I have found this basalt rock on a field but it is different than i am used to. Caracteristiks: heavy for it's size and has vugs in stead of vesicles which are filled with elongated white crystals and it atract a magnet strongly, small pieces of the rock jump on the magnet. Alle the white bits you see are crystals

 

[Mackaydon]

Regarding the gray piece on the left, Google Lens says it "shows a vesicular texture (small cavities formed by gas bubbles) and is light gray, likely due to weathering or alteration rather than its typical dark color."
Don in SoCal

 

[rockcollect]

Regarding the gray piece on the left, Google Lens says it "shows a vesicular texture (small cavities formed by gas bubbles) and is light gray, likely due to weathering or alteration rather than its typical dark color."
Don in SoCal

thank you for your answer, all the photo's are of the same rock. And if i understand correctly vesicles are smooth and round and vugs are irregular and elongated, the last is what my basalt has.

 

[rockcollect]

closeups outside and inside of the rock

 

[rockcollect]

I have found only one match with my rock and that is
Basaltina Classico is a natural volcanic stone found exclusively in the Viterbo region of Central Italy, specifically near the town of Bagnoregio in the Lazio area.

Location: The quarry is located at Loc. Ponzano, Bagnoregio (VT), a region known for its ancient volcanic activity and proximity to Bolsena Lake.
Production: This stone is quarried in the form of large, irregular boulders that display natural horizontal stratification.
Type & Name: Basaltina Classico (also known as Basaltina Tipo Classico or Pietra Basaltina) is a type of lava stone used for centuries, with the main quarry established in the Bagnoregio area.

My rock has horizontal vugs as has basaltina classico.But here is the catch, the italian rock is only found in one place in the whole world see discription. So my rock is pretty unique i believe. see photo comparison of my rock and the italian rock.

 

[rockcollect]

more info about the basalt from Italy: https://www.mindat.org/loc-283320.html

 

[Red-Coat]

Hi @rockcollect

Responding to you request for me to take a look at this thread.

I would still term this as vesicular basalt, even though the vesicles are not the more typical round bubbles. Vesicular basalts arise from mafic lava that has cooled rapidly at or near the Earth’s surface, the bubbles being formed by expansion of gases or water vapour. When the vesicles are stretched or elongated, creating a pitted texture, it’s an indication that the lava was still moving as it cooled. Note that there is a high degree of alignment in your rock with the vesicles acting as ‘strain markers’ which indicate directional flow.

Whether elongated or not, these voids can become lined or filled with secondary material when mineral-rich groundwater permeates them. The most common secondary deposits in basalts are calcite, chalcedony, quartz, or zeolites. When the cavities are completely filled, the features are termed ‘amygdules’ and the resultant rock as ‘amygdaloidal basalt’.

Some people use the terms vug and vesicle interchangeably or refer to all non-spherical vesicles as vugs, especially when lined with crystalline secondary minerals as ‘drusy’ deposits. Others use a more precise geological definition that vugs form later in a rock’s history by tectonic movement or dissolution of existing minerals (which can then also re-fill with a replacement mineral). Either way, a stretched void left by a gas bubble in lava that later fills with crystals can sometimes be considered both as a vesicle and a vug.

 

[rockcollect]

Again WOW super detailed information and excelent explenation. Are you a geologist ? And yes the voids are filled with crystal elongated and translucent and perfecty formed. i can´t photograph it sadly. But they are not completely filled and the crystals grow in clusters.

 

[Red-Coat]

Again WOW super detailed information and excelent explenation. Are you a geologist ?

You're welcome. No, I'm not a geologist by profession or education. Just an experienced amateur.

 

[rockcollect]

You're welcome. No, I'm not a geologist by profession or education. Just an experienced amateur.

Dear Red-coat, you mentioned the high degree of alignment in my rock, but i have google it in many terms but can not find any examples of basalt that have that feature. Is that feature rare or common? I have also noticed that the rock has pale yellow olivine crystals with a black glassy rim. Do you know how that forms?

 

[Red-Coat]

Dear Red-coat, you mentioned the high degree of alignment in my rock, but i have google it in many terms but can not find any examples of basalt that have that feature. Is that feature rare or common? I have also noticed that the rock has pale yellow olivine crystals with a black glassy rim. Do you know how that forms?

This schematic from Alex Strekeisen’s website explains how magmatic flow can influence alignment. Although the diagram specifically references the effect on crystalline minerals within a basaltic magma, exactly the same effects influence the stretching and/or flattening of vesicles in rocks such as basalt, whether the vesicles become crystal-lined or not.

No, it’s not particularly common and depends entirely on the mass, density and viscosity of the magma, the pressures that forced it to the surface, its temperature, and the rate at which it cooled to below solidification point.

You can see the effect very clearly in this sample of porphyritic basalt (picture from Michigan Tech Keweenaw Geoheritage website) with crystalline flow-markers:

This microphotograph (University of Durham, Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence) shows an elongated vesicle in basalt that has become crystal-lined:

This one (also from Alex Strekeisen’s website) shows an undistorted vesicle with a crystalline lining. The deposits are usually the result of low-temperature alteration of minerals from groundwater, with the concentric deposits being zoned and progressively growing inwards from the walls of the vesicle as a result of variations in water penetration. The banded colour variations are not always because the minerals are different, but sometimes arise from differential staining as a result of those variations.

 

[russau]

WOW what a detailed explanation !!!!!! VERY GOOD Red - Coat !!!!!!