Also OP I don't think your desire to have a stone is pathological and am a little frustrated for you that he has suggested it is pathological and caused you such anxiety about it, that something that should have been a small thing, a minor gesture of support, has become such a big deal between the both of you. Some people are sentimental and like to hold on to things that remind them of other people and places that make them feel safe or carry good feelings. I have bones and rocks on my desk from places I have visited, for example, or small items that remind me of friends. Rubbing smooth stones itself is therapeutic for anxiety, but especially if it is attached to a safe or happy place or person.

Therapy is meant to be such a place, in a way. As is common, when we started doing trauma work and I started panicking my therapist helped me find grounding memories of "safe places" to bring to mind when I am beginning to feel overwhelmed. He emphasizes that he wants to make the room a "safe place." You have very high anxiety and abandonment fears and a stone you can hold that reminds you of your therapist/the therapy room is a coping object. He could see it as a positive thing and encourage you to hold the stone instead of emailing him again when he hasn't emailed back, for example. If he knows you SH, this is especially weird. SH is the maladaptive mechanism and carrying/holding a stone is the healthy one--if the latter could help prevent the former then he should not be making you feel bad about needing it.

I think sometimes people don't consider the necessary distinction between "normal" or "common" and "pathological." No, most people don't need a transitional object from their therapist, just as most people don't need a cadre of happy memories in store to keep them from having a panic attack when triggered; I don't see how an object that eases the pain of separation for the unhealthily attached client outside the therapy room is maladaptive and necessary to "correct." I get that you are working on attachment in addition to anxiety and he is worried about dependency, but you still need a way to deal with these negative feelings when they get overwhelming. SH is harmful, the stone is healthy. There is literally something called a Worry Stone that is marketed and sold. So I just don't get it, unless there's something I'm missing.