GeologyRocks

It look like a bit of a volcanic bomb to me.  Perhaps one that was either brittle from that particular chemistry, or was ejected to a great height and shattered on impact. 

John

“Civilisation exists by geological consent, subject to change without notice.” -  Will Durant

That is just awesome. I have 3 pieces.

Is it rare or very common? 

 Sadly they are quite common Ronnie.  So much so that I only have to drive 20 miles from here to collect them from the remnants of an Ordovician volcano.  And they are the proper twisted elongated bombs - lava which has twisted at high speed trough the air during an eruption. Google images of lava bombs and you'll see what I mean. 

Having said that  yours are just as valuable to you, because you found them!

John

“Civilisation exists by geological consent, subject to change without notice.” -  Will Durant

Well, even if they are common, as you said, for me they are some treasure.But I don't even find some very common rocks like obsidian , flint and iron ore! 

Don't expect too much! 

No all eruption will produce obsidian.  Obsidian form when magma/lava is cooled very very quickly.   That really implies that there is snow, ice or cold water in the immediate vicinity.

 You are unlikely to find flint in the proximity of a volcano, since it forms in sedimentary rocks - usually chalk.   There is a lot of controversy about how flint forms, but the most popular is that it is the silica  from sponges.

Iron?  You may well have a percentage of iron within that lava bomb.   It depends on the volcanoes chemical signature.  But you won't find it there in ore form.

 There are many iron bearing ores.  The one richest in Fe is hematite, but geothite contains some as does siderite and a number of others. 

John

“Civilisation exists by geological consent, subject to change without notice.” -  Will Durant

Umm I didn't wanted to say that i would like to find those rock NEAR this volcano. I just talked about my regular life.

After all, I'm proud to have some rocks and minerals that I found.My friends are collecting too, but they are buying them.

There are some minerals which you will never get in your own country, or even those you can afford to travel to.  I feel that in cases like that buying is fine. 

Also you are unlikely to find things of an equivalent quality to that which a mineral dealer sells, unless you have access to mines.

There are those which only occure in the type locallity.  As far as UK goes :-

mendipite and with the mendipite you will always find parkinsonite (the purplish sheen with the xls only visible with electron scanning).  

There is a type of baryte found only 20 miles from me which is found nowhere else in the world (celestobaryte - it is pink to red, radiating xls), and in Derbyshire there is one called 'oakstone' baryte, from Youlgrave, which is no longer quarried/mined (not sure which, but they stopped digging in 1972).  Cut through and polished it resembles a piece of wood, the nearest comparrison being oak.

Lapis lazuli is only found in Afghanistan, although there is a poor seam in Chile.  But the Afghan mine has been worked since Alexander The Greats time and there is only about 10 years worth left.  The Chilean seam just matches the lowest grade from Afghanistan.

There will be oddities in your country - although I can't think of one right now. 

John

“Civilisation exists by geological consent, subject to change without notice.” -  Will Durant