Usually, but I won't guarantee all the time, if you are looking at the book from the Amazon web site in a browser, under Product Details if there is NOT a file size listed then the book is likely Topaz. Example, a current freebie: Faces of Betrayal (
link here)
Product Details
* Format: Kindle Edition
* Print Length: 320 pages
* Publisher: Thomas Nelson (April 7, 2009)
* Sold by: Amazon Digital Services
* Language: English
* ASIN: B0024NLHSA
You see it shows a print length, but no file size. So it is probably (and did turn out to be) Topaz.
In contrast, another freebie (Goddess of Fried Okra) shows:
Product Details
* Format: Kindle Edition
* File Size: 518 KB
* Print Length: 242 pages
* Publisher: BelleBooks - A (March 30, 2010)
* Sold by: Amazon Digital Services
* Language: English
* ASIN: B003EO8EVG
So it lists File size and is likely NOT Topaz and is a regular azw/mobi file.
I forget if this holds true when browsing the store from your actual Kindle. I do most of my browsing from the website.