asbestos in walls? (photo attached)

I have worked with asbestos for many years. However it was not friable or airborne so I never gave it a second thought. An expert in asbestos abatement will likely respond soon. In the meantime here is my take. Don't disturb the material further until you know for sure that there is no asbestos present. When in doubt, assume the contaiminant is there. Remove a small sample and send it to a lab for analysis if recommended by an expert. The Internet can help you locate a lab. Close off the room using plastic and tape. If there are air vents tape them shut too. Launder any clothing that may have the particles on them. I expect someone to suggest that such a cautious approach is not needed. I would not panic but I would take it seriously. Asbestos was once commonly used in many products such as floor tiles and pipe wrap and the absence of visible fibers is not conclusive. I have seen asbestos under a microscope and each fiber had tiny barbs like fishhooks. It is my understanding that those barbs make it difficult to exhale the fibers once they enter the lungs. The age of the material may offer a clue as to the likelihood that asbestos is present.