Featured What material could this be? What’s the thing on the front?

Density != weight neccessarily. Organic matter especially can be close packed, but because you're dealing with basically cellulose, it's light.

 

I just pulled out the one bog oak piece I have on hand. Size is comparable to yours & it is quite light.

 

To my eye, both front and back appear to show pressed horn rather than bog oak - this sales description shows the same 'bog oak' brooch as Debora posted, described as 'pressed horn':

https://downadarkalley.com/product/gorgeous-antique-victorian-pressed-horn-mourning-brooch/




~Cheryl

 

I was thinking horn might have an odor to it but just a thought

 

For easier comparison:




The center plaquette of these looks like a separate piece. You can see this in the brooch at Cheryl's link:



So I think there are 2 questions for these pieces. What is the press molded plaquette made of? What is the outer frame made of?

On the back of the brooch represented as pressed horn (how thick can pressed horn be?) I do not see the woody grain of the original brooch. The body of the first one still looks like bog oak to me. If I had only the photos with no further info, I would think the main part of the horn one was jet. (I should state here, not for the last time, that I hate trying to identify black stuff.) I would also conclude that both brooches have a central element, which may very well be pressed horn, from the same source. Like cameos of Headband Girl, the little plaques may have been manufactured in a separate operation & sold for the making of the finished jewellery.

 

In these pics the round one is horn and 2nd big oak? @Bronwen

 

The round one is the one from the link Cheryl posted right before that is being offered as pressed horn. The second pic is the back of your brooch. To my eye, from the back the 2 do not look like the same material & yours still looks like bog oak to me. On the other hand, the central elements on both brooches look made by the same process, in the same material, perhaps from the same manufacturer. I have no trouble believing the plaquettes are pressed horn. I just think they may have been set into brooches of different materials, including pressed horn, jet & bog oak.

Not making much headway because they all still just look black to me, but in trying to do some eye training, found this great site:

https://www.modip.ac.uk/search?search=pressed horn&page=0