GeologyRocks

Permineralisation is not a term we use over here - at least I have never heard it used.  We simply refer to replacement minerals in fossils.

I am not sure what you mean by the second part of your question.  It is extremely hard for dead creatures to be fossilised.  Conditions have to be right. They have to be buried fairly quickly (before they can be scavenged) in anaerobic conditions  (oxygen free).  This is why tar pits produce amazingly preserved creatures.

What the mineral replacement is will depend on the hypogenic fluids in that place being deposited  before the specimen decays completely.

Usually it is silica (quartz replacement), calcium (calcite replacement) or iron (pyrite replacement).  There are others which are much rarer.  Currently I have an ammonite sp Perishinctus for sale, which is replaced with copper.  Never seen that before, but a friendly palaeontologist (yes, such creatures do exist) assures me that it is rare, rather than unheard of.

 John

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

Replacement minerals. ok. Let's imagine for a second, that a large vertebrate fossil from the Jurassic Period had been petrified in much the same manner as petrified wood, under perfect conditions. Say, instantly buried by volcanic debris, or fallout from a nearby meteorite strike, Would the DNA of the fossil still be preserved around the Lumens of veins, arteries, and cellular wall structure, as it is with certain specimens of petrified wood?

I've read up on permineralization on wikipedia, and it is peaking my interest as it says on ultra rare cases, fossils that have been permineralized, may contain alot of the original DNA.

In rare permineralization cases it states that the Lumens in veins are mineralized, While the surrounding vessel walls are still intact, visible, and has most of the original cell structure.

Alot of people are unaware of permineralized fossils, or replacement minerals. Since finding a fossil that has actually been permineralized is so incredibly rare. Aside ammonite that is.

Well, if thats what Wikipedia says so be it. 

 John

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

That sounds like a very cool ammonite you have. Is it colorful? 

I'm not a geologist by any means, ive worked with geologists/hydrogeologists/archaeologists etc, drilling in various parts of northern canada. I joined this forum to seek information for my own interest. Wikipedia is very general when it comes to getting a real experts understanding or view on a particular subject. This is a subject that interests me, as it seems to be fairly rare. I respect any advice or knowledge that is given by you or anyone else with much greater understanding than I, on the subject.

My next question is, is it possible to have two different types of mineral replacement within the same host rock or fossil? EG. silica replacement as well as a seperate calcium mineral replacement?

No.  Its a creamy off-white (usual Perisphinctus colour), about 1"  dia.,  but the copper shows nicely towards the centre. 

BTW - I believe I have seen silica and calcite in the same specimen, but the calcite must have been secondary because of the differences in heat between the two.

However.......There is a quarry just outside Wells in Somerset where 'potato stones' were dug up. These could be geodes or totally infilled, but you had to take them to the quarry shop and pay £1 per lb for them unopened.  They had very clear quartz crystal on the lining and sort of 'webs' of quartz crystals across.  There was always some calcite, and often a complete infill of it. But putting it in a bucket of HCl got rid of the calcite nicely, and often there would be some double terminated quartz crystals.  This suggests that those crystals came later and were able to form completely within the 'softer' Ca.  I have never quite understood it and a booklet written on 'Dulcot Potato Stones & Bristol Diamonds' simply skirts over it.  The whole bed has now been dug out, although there are locations in the Mendips where the Potato stones can still be foud, but only very small ones.

No one can visit Dulcot Quarry any more, although at one time it wasa frequent visiting place, with all the geological clubs in UK invited for a barbi annually  - or once a year, whichever came sooner.  We all signed to say we would make no claim on Foster-Yeomans (quarry owners) if we got injured, but a German club came over, and someone twisted or broke his ankle and tried to make a claim.  Hence no one is allowed in now. 

John

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