Diamonds can be produced in a lab. Unlike cubic zirconoia, these diamonds are molecularly identical to naturally occuring diamonds (and rival natural diamonds for clarity.
Now the diamond associations are asking the FTC that such diamonds be referred to as synthetic diamonds and not cultured diamonds. Cultured diamond creators argue that their process is analogous to that used for creating cultured pearls, in that the gem is created not by ‘synthesizing’ but by reproducing natural processes (WSJ reg req).

2d Circuit decision in Louis Vuitton v Burlington Coat Factory discussing proper application of the Polaroid factors (the test of likelihood of confusion in these parts):
In applying the Polaroid factors during resolution of the parties’ claims at a trial
on the merits, the District Court should consider not only the potential for consumer
confusion as to the source of the marks in question, but should also consider the potential for confusion as to the “sponsorship, affiliation, connection, or identification” of those marks. Star Indus. v. Bacardi & Co., 412 F.3d 373, 383 (2d Cir. 2005). The District Court should give particular attention to the Polaroid factors in light of the potential for types of confusion other than source confusion, focusing perhaps especially on (1) the proximity of the products and their competitiveness with one another, (2) evidence that the imitative mark was adopted in bad faith, and (3) sophistication of consumers. See, e.g., Lois Sportswear, U.S.A., Inc. v. Levi Strauss & Co., 799 F.2d 867, 874-75 (2d Cir. 1986); Sports Auth. v. Prime Hospitality Corp., 899 F.3d 955, 964 (2d Cir. 1996). In considering both source and non-source confusion, the district court should ensure it gives adequate weight to the strength of the Louis Vuitton trademark when weighing the various Polaroid factors. See Louis Vuitton Malletier v. Dooney & Bourke, Inc., 454 F.3d 108, 116 (2d Cir. 2006). Finally, we note that the potential for non- source confusion and its applicability to the Polaroid factors may be relevant to Louis Vuitton’s claims under New York’s anti-dilution statute, New York General Business Law Section 15 360-l (McKinney Cum. Supp. 2007). See Hormel Foods Corp. v. Jim Henson Prods., 73 F.3d 497,16 506-08 (2d Cir. 1996).
UPDATE: An amended order has been issued correcting errors.